Method for reproducing information data from magneto-optical recording medium using linear polarized beam

ABSTRACT

A method for reproducing write-once information from an optical disk. The disk includes a disk substrate and a recording layer on the disk substrate, the recording layer including a magnetic film with a magnetic anisotropy in a direction perpendicular to a surface of the magnetic film. Write-once information formed by first recording areas and second recording areas is stored in a pre-determined portion of said recording layer, the first and second recording areas having different magnetic anisotropies in a direction perpendicular to a surface of the magnetic film. The method includes irradiating linearly polarized laser light onto said pre-determined portion, and detecting a rotational change in a polarization orientation of light reflected from the optical disk or light transmitted through the optical disk, the rotational change being caused depending on which of the first recording area and the second recording area is irradiated with the linearly polarized laser light.

This application is a divisional of application Ser. No. 09/308,550,filed May 20, 1999, which is a 371 of PCT/JP97/04664, filed Dec. 17,1997 which application(s) are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an optical disk for recording,reproducing and erasing information. In particular, the presentinvention relates to an optical disk comprising write-once informationthat can be used for copyright protection, for example forcopy-protection or protection from unauthorized use of software.Throughout this specification, “write-once information” refers toinformation that is recorded after finishing the disk manufacturingprocess. The present invention relates further to a method for recordingand a method for reproducing write-once information on the optical disk,an apparatus for reproducing the optical disk, an apparatus forrecording and reproducing the optical disk, an apparatus for recordingwrite-once information on the optical disk, and an apparatus forrecording on the optical disk.

BACKGROUND OF THE INVENTION

In recent years, the speed with which electronic calculators andinformation processing systems can process ever greater amounts ofinformation has increased sharply. Together with the digitalization ofaudio and video information, this gave rise to the rapid disseminationof low-cost, high-volume auxiliary storage devices and recording mediatherefor, especially optical disks, which can be accessed with highaccess speeds.

The basic configuration of conventional optical disks is as follows: Adielectric layer is formed on top of a disk substrate, and a recordinglayer is formed on top of the dielectric layer. On top of the recordinglayer, an intermediate dielectric layer and a reflecting layer areformed in that order. An overcoat layer is formed on top of thereflecting layer.

The following is an explanation of how an optical disk with the aboveconfiguration is operated.

In the case of an optical disk having, in its recording layer, amagneto-optical layer with perpendicular magnetic anisotropy, therecording and erasing of information is performed by locally (a) heatingthe recording layer with a laser beam to a temperature with smallcoercive force above the compensation temperature or to a temperaturenear or above the Curie temperature to decrease the coercive force ofthe recording layer in the irradiated portion, and (b) magnetizing therecording layer in the direction of an external magnetic field. (This isalso called “thermomagnetic recording” of information.). Moreover, forthe reproduction of the recording signal, a laser beam with lessintensity than the laser beam for recording or erasing irradiates therecording layer. The recording state of the recording layer, that is,the rotation of the polarization plane of the light that is reflected ortransmitted in accordance with the orientation of the magnetic field(this rotation occurs mainly due to two magneto-optical effects—the Kerreffect and the Faraday effect), is detected by a photodetector throughthe change in the intensity of the irradiated light. In order todecrease the interference between opposite magnetizations and allowhigh-density recordings, a magnetic material with perpendicular magneticanisotropy is used for the recording layer of the optical disk.

Moreover, when the data is reproduced, the reproduction signal levelduring data reproduction can be raised to detect the reproduction signalby using a layered structure for the recording layer: Several magneticthin films comprising an exchange coupling multilayer or amagneto-static coupling multilayer.

For the recording layer, a material is used that can record informationby locally raising the temperature or inducing a chemical reaction dueto absorption of the irradiated laser light. The local variations in therecording layer can be detected by irradiating laser light of adifferent intensity or wavelength than that used for the recording anddetecting the reproduction signal using the reflected or the transmittedlight.

Regarding such optical disks, there is a need for a way to protect thedata on the disk with write-once information (identification data) thatallows for copyright protection, for example copy protection andprotection against unauthorized use of software.

With the above configuration, it is possible to record disk informationin TOC (or control data) areas, but when disk data is recorded withpre-pits, the disk information has to be administered stamper by stamperand cannot be administered user by user.

Moreover, when information is recorded using a magnetic film or a filmof a phase-reversible material, administrative information easily can bechanged, which means that it easily can be rewritten (manipulated), sothat the contents on the optical disk cannot be copyright protected.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the problems of theprior art. It is a further object of the present invention to provide anoptical disk comprising write-once information that can be used forcopyright protection, for example for copy-protection or protection fromunauthorized use of software, a method for recording write-onceinformation on an optical disk, a method for reproducing write-onceinformation from an optical disk, an apparatus for reproducing opticaldisks, an apparatus for recording and reproducing optical disks, anapparatus for recording write-once information on optical disks, and anapparatus for recording on optical disks.

In order to attain these objects, a first configuration of an opticaldisk in accordance with the present invention comprises a disk substrateand a recording layer on the disk substrate. The recording layerincludes a magnetic film with a magnetic anisotropy in a directionperpendicular to a surface of the magnetic film. The optical disk storeswrite-once information formed by first recording areas and secondrecording areas in a pre-determined portion of the recording layer. Amagnetic anisotropy in a direction perpendicular to a surface of thesecond recording areas is smaller than a magnetic anisotropy in adirection perpendicular to a surface of the first recording areas. Thesecond recording areas are formed as strip-shaped marks that are oblongin a radial direction of the disk. A plurality of the marks is arrangedin a circumferential direction of the disk, the arrangement being basedon a modulation signal of the write-once information. In accordance withthis first configuration, an optical disk can be achieved, whichcomprises write-once information that can be used for copyrightprotection, for example for copy-protection or protection fromunauthorized use of software.

It is preferable that the optical disk according to the firstconfiguration further comprises an identifier indicating whether thereis a row of a plurality of marks arranged in a circumferential directionof the disk. With this configuration, the system can be started in ashort time. Moreover, in this configuration, it is preferable that theidentifier indicating the row of marks is stored among control data.With this configuration, it is known when the control data is reproducedwhether write-once information is stored, so that the write-onceinformation can be reproduced reliably.

It is preferable that in the optical disk according to the firstconfiguration, the pre-determined portion comprising write-onceinformation is at an inner perimeter portion of the disk. With thisconfiguration, the position of the optical head with respect to a radialdirection of the disk can be determined with an optical head stopper oraddress information of a bit signal.

It is preferable that in the optical disk according to the firstconfiguration, a difference between a luminous energy that is reflectedfrom the first recording areas and a luminous energy that is reflectedfrom the second recording areas is below a certain value. It isparticularly preferable that the difference between luminous energy thatis reflected from the first recording areas and luminous energy that isreflected from the second recording areas is not more than 10%. Withthis configuration, variations of the reproduction waveform accompanyingchanges of the reflected luminous energy can be suppressed.

It is preferable that in the optical disk according to the firstconfiguration, a difference between an average refractive index of thefirst recording areas and an average refractive index of the secondrecording areas is not more than 5%. With this configuration, thedifference between luminous energy that is reflected from the firstrecording areas and luminous energy that is reflected from the secondrecording areas can be adjusted to not more than 10%.

It is preferable that in the optical disk according to the firstconfiguration, the magnetic anisotropy of the magnetic film of thesecond recording areas in an in-plane direction is dominant. With thisconfigurations using a reading device having a polarizer and aphoto-detector the reproduction signal of the first recording areas,which corresponds to the write-once information, can be attained. Thus,the write-once information can be obtained rapidly and without using anoptical head.

It is preferable that in the optical disk according to the firstconfiguration, at least a portion of the magnetic film of the secondrecording areas is crystallized. With this configuration, the magneticanisotropy perpendicular to the magnetic film of the second recordingareas can be almost completely eliminated, so that the reproductionsignal can be reliably detected as the difference of the polarizationorientation to the first recording areas.

It is preferable that in the optical disk according to the firstconfiguration, the recording layer comprises a multilayer magnetic film.With this configuration, the magnetically induced super resolutionmethod “FAD” can be used as the reproduction method. Thus, signalreproduction with regions smaller than the laser beam spot becomespossible.

A second configuration of an optical disk in accordance with the presentinvention comprises a disk substrate and a recording layer on the disksubstrate. The recording layer includes a film that can be reversiblychanged between two optically detectable states. The optical disk storeswrite-once information formed by first recording areas and secondrecording areas in a predetermined portion of the recording layer. Aluminous energy that is reflected from the first recording areas differsfrom a luminous energy that is reflected from the second recordingareas. The second recording areas are formed as stripe-shaped marks thatare oblong in a radial direction of the disk. A plurality of the marksis arranged in a circumferential direction of the disk, the arrangementbeing based on a modulation signal for the write-once information. Inaccordance with this second configuration, an optical disk can beachieved, which comprises write-once information that can be used forcopyright protection, for example for copy-protection or protection fromunauthorized use of software.

It is preferable that the optical disk according to the firstconfiguration further comprises an identifier for indicating whetherthere is a row of a plurality of marks arranged in a circumferentialdirection of the disk. Moreover, it is preferable that the identifierindicating the row of marks is stored among control data.

It is preferable that in the optical disk according to the firstconfiguration, the pre-determined portion comprising write-onceinformation is at an inner perimeter portion of the disk.

It is preferable that in the optical disk according to the firstconfiguration, the recording layer undergoes a reversible phase changebetween a crystalline phase and an amorphous phase, depending onirradiation conditions for irradiated light. With this configuration,information can be recorded by utilizing an optical difference based ona reversible structural change at the atomic level. Moreover,information can be reproduced as a difference of the reflected luminousenergy or the transmitted luminous energy at a certain wavelength.Moreover, in this case, it is preferable that the difference betweenluminous energy that is reflected from the first recording areas andluminous energy that is reflected from the second recording areas is atleast 10%. With this configuration, a reproduction signal of the firstrecording area, which corresponds to the write-once information, can beobtained reliably. Moreover, in this case, it is preferable that adifference between an average refractive index of the first recordingareas and an average refractive index of the second recording areas isat least 5%. With this configuration, the difference between theluminous energy reflected from the first recording areas and theluminous energy reflected from the second recording areas can beadjusted to at least 10%. Moreover, in this case, it is preferable thatthe second recording areas of the recording layer are in a crystallinephase. With this configuration, recording can be performed withexcessive laser power. Furthermore, since the luminous energy reflectedfrom the crystalline phase can be large, detection of the reproductionsignal becomes easy. Moreover, in this case, it is preferable that therecording layer comprises a Ge—Sb—Te alloy.

In a third configuration of an optical disk in accordance with thepresent invention, main information and write-once information isrecorded, the write-once information being different for each disk, andthe write-once information storing at least watermark productionparameters for producing a watermark. In accordance with this thirdconfiguration, the following operations can be performed: When thewatermark production parameters and the disk ID are recorded in thewrite-once information with absolutely no correlation between the diskID and the watermark production parameters, it becomes impossible toguess the watermark from the disk ID. Thus, an illegal copier issuing anew ID and issuing an improper watermark can be prevented.

It is preferable that in the optical disk according to the thirdconfiguration, the main information is recorded by providingconvex-concave pits in a reflective layer, and the write-onceinformation is recorded by partially removing the reflective layer.

It is preferable that in the optical disk according to the thirdconfiguration, the main information and the write-once information arerecorded by partially changing a reflection coefficient of a reflectivelayer.

It is preferable that in the optical disk according to the thirdconfiguration, a recording layer comprises a magnetic layer with amagnetic anisotropy in a direction perpendicular to a surface of themagnetic layer, the main information is recorded by partially changing amagnetization direction of the recording layer, and the write-onceinformation is recorded by partially changing the magnetic anisotropy inthe direction perpendicular to the surface of the magnetic layer.

A first method for recording write-once information onto an optical disk(a) comprising a disk substrate, and a recording layer on the disksubstrate, including a magnetic film with a magnetic anisotropy in adirection perpendicular to a surface of the magnetic film; and (b)storing write-once information formed by first recording areas andsecond recording areas in a pre-determined portion of the recordinglayer; comprises forming the second recording areas as a plurality ofstripe-shaped marks that are oblong in a radial direction of the disk ina circumferential direction of the disk by irradiating laser light basedon a modulation signal of the write-once information in acircumferential disk direction in the pre-determined portion of therecording layer in a manner that a magnetic anisotropy in a directionperpendicular to a surface of the second recording areas becomes smallerthan a magnetic anisotropy in a direction perpendicular to a surface ofthe first recording areas. In accordance with this first method forrecording write-once information onto an optical disk, write-onceinformation that can be used for copyright protection, for example forcopy-protection or protection from unauthorized use of software, can beefficiently recorded onto an optical disk.

It is preferable that in the first method for recording write-onceinformation, when the second recording areas are formed, a laser lightsource is pulsed in accordance with a modulation signal of phase-encodedwrite-once information, and the optical disk or the laser light isrotated. With this configuration, rotation variations can be eliminated,especially when the clock of a rotation sensor is used, so that thewrite-once information can be recorded with little fluctuations of thechannel clock period.

It is preferable that in the first method for recording write-onceinformation, the optical disk further comprises a reflective layer and aprotective layer on the disk substrate, and an intensity of laser lightirradiated to form the second recording areas is smaller than anintensity of laser light destroying at least one of the disk substrate,the reflective layer and the protective layer. With this configuration,write-once information can be recorded at software companies orretailers.

It is preferable that in the first method for recording write-onceinformation, an intensity of laser light irradiated to form the secondrecording areas is an intensity for crystallizing at least a portion ofthe recording layer. With this configuration, the magnetic anisotropy ofthe recording layer perpendicular to the surface of the recording layercannot be restored, so that manipulation of the write-once informationcan be prevented.

It is preferable that in the first method for recording write-onceinformation, an intensity of laser light irradiated to form the secondrecording areas is larger than an intensity of laser light heating therecording layer to a Curie temperature. With this configuration, it ispossible to decrease or eliminate the magnetic anisotropy of therecording layer perpendicular to the surface of the recording layer,especially when the intensity of the laser light is excessive.

It is preferable that in the first method for recording write-onceinformation, an intensity of laser light irradiated to form the secondrecording areas is an intensity for making a magnetic anisotropy of themagnetic layer of the first recording areas in an in-plane directiondominant.

It is also preferable that in the first method for recording write-onceinformation, rectangularly stripe-shaped laser light is irradiated witha unidirectional convergence focusing lens onto the recording layer whenthe second recording areas are formed.

It is also preferable that in the first method for recording write-onceinformation, a light source of the laser light that is irradiated forforming the second recording areas is a YAG laser. In this case, it ispreferable that a magnetic field above a certain value is applied to therecording layer while irradiating laser light from the YAG laser. Withthis configuration, write-once information can be recorded easily bypartially changing the magnetic anisotropy perpendicular to the surfaceof the recording layer after aligning the magnetic anisotropy in adirection perpendicular to the surface of the recording layer. In thiscase, it is even more preferable that the magnetic field applied to therecording layer is at least 5 kOe.

A second method for recording write-once information onto an opticaldisk (a) comprising a disk substrate; and on the disk substrate arecording layer comprising a film that can be reversibly changed betweentwo optically detectable states; and (b) storing write-once informationformed by first recording areas and second recording areas in apre-determined portion of the recording layer; comprises forming thesecond recording areas as a plurality of stripe-shaped marks that areoblong in a radial direction of the disk in a circumferential directionof the disk by irradiating laser light based on a modulation signal ofthe write-once information in a circumferential disk direction in thepre-determined portion of the recording layer in a manner that aluminous energy of light reflected from the first recording areasdiffers from a luminous energy of light reflected from the secondrecording areas. In accordance with this second method for recordingwrite-once information onto an optical disk, write-once information thatcan be used for copyright protection, for example for copy-protection orprotection from unauthorized use of software, can be efficientlyrecorded onto an optical disk.

It is preferable that in the second method for recording write-onceinformation, when the second recording areas are formed, a laser lightsource is pulsed in accordance with a modulation signal of phase-encodedwrite-once information, and the optical disk or the laser light isrotated.

It is also preferable that in the second method for recording write-onceinformation, the optical disk further comprises a reflective layer and aprotective layer on the disk substrate, and an intensity of laser lightirradiated to form the second recording areas is smaller than anintensity of laser light destroying at least one of the disk substrate,the reflective layer and the protective layer.

It is also preferable that in the second method for recording write-onceinformation, an intensity of laser light irradiated to form the secondrecording areas is an intensity for crystallizing at least a portion ofthe recording layer.

It is also preferable that in the second method for recording write-onceinformation, rectangularly stripe-shaped laser light is irradiated ontothe recording layer with a unidirectional convergence focusing lens whenthe second recording areas are formed. In this case, it is alsopreferable that a light source of the laser light that is irradiated forforming the second recording areas is a YAG laser.

A third method for recording write-once information onto an optical diskcomprises producing a watermark based on a disk ID; and overlapping thewatermark on specific data to record it as write-once information. Inaccordance with this third method for recording write-once informationonto an optical disk, the disk ID can be detected from the watermark, sothat the origin of illegal copies can be determined.

A first method for reproducing write-once information from an opticaldisk (a) comprising a disk substrate, and a recording layer on the disksubstrate, the recording layer including a magnetic film with a magneticanisotropy in a direction perpendicular to a surface of the magneticfilm; and (b) storing write-once information formed by first recordingareas and second recording areas in a pre-determined portion of therecording layer, the first and second recording layers having differentmagnetic anisotropies in a direction perpendicular to a surface of themagnetic layer; comprises irradiating linearly polarized laser lightonto the pre-determined portion; and detecting a change in apolarization orientation of light reflected from the optical disk orlight transmitted through the optical disk. In accordance with thisfirst method for reproducing write-once information from an opticaldisk, the write-once information can be reproduced easily.

It is preferable that in the first method for reproducing write-onceinformation, the linearly polarized laser light is irradiated onto thepre-determined portion after magnetizing the recording layer of thepre-determined portion in one step by applying a magnetic field that islarger than a coercive force of the recording layer in thepre-determined portion. With this configuration, the polarizationorientation detected from the first recording areas is normallyconstant, and the reproduction signal can be obtained with a stableamplitude from the difference with respect to the polarizationorientation of the second recording areas.

It is also preferable that in the first method for reproducingwrite-once information, the linearly polarized laser light is irradiatedonto the pre-determined portion after aligning a magnetization of therecording layer of the pre-determined portion by applying aunidirectional magnetic field to the predetermined portion whileincreasing the temperature of the recording layer in the pre-determinedportion above the Curie temperature by irradiating laser light ofconstant luminous energy. With this configuration, after recording thewrite-once information, the signal can be reliably reproduced withoutbeing influenced by outside magnetic fields or the like.

A second method for reproducing write-once information from an opticaldisk (a) comprising a disk substrate; and a recording layer on the disksubstrate, the recording layer including a film that can be reversiblychanged between two optically detectable states; and (b) storingwrite-once information formed by first recording areas and secondrecording areas with different reflection coefficients in apre-determined portion of the recording layer; comprises irradiatingfocused laser light onto the pre-determined portion; and detecting achange in a luminous energy reflected from the disk. In accordance withthis second method for reproducing write-once information from anoptical disk, the write-once information can be reproduced easily.

A first configuration of an apparatus for reproducing optical diskscomprising (a) a main information recording area for recording maininformation; and (b) an auxiliary signal recording area overlappingpartly with the main information recording area for recording aphase-encoding modulated auxiliary signal that overlaps a signal of maininformation, comprises means for reproducing a main information signalin the main information recording area with an optical head; firstdecoding means for decoding a main information signal to obtain maininformation data; means for reproducing a mixed signal comprising a maininformation signal in the auxiliary signal recording area and theauxiliary signal as a reproduction signal with the optical head;frequency separation means for suppressing the main information signalin the reproduction signal to obtain the auxiliary signal; and seconddecoding means for phase-encoding decoding the auxiliary signal toobtain the auxiliary data. In accordance with this first configurationof an apparatus for reproducing optical disks, the decoding data of theauxiliary signal can be reproduced reliably.

It is preferable that in the apparatus for reproducing optical disksaccording to the first configuration, the frequency separation means isa low-frequency component separation means for suppressing highfrequency components in the reproduction signal reproduced with theoptical head to obtain a low frequency reproduction signal, and that theapparatus further comprises a second-slice-level setting portion forproducing a second slice level from the low-frequency reproductionsignal; and a second-level slicer for slicing the low-frequencyreproduction signal at the second slice level to obtain a binarizedsignal; wherein the apparatus phase-encoding decodes the binarizedsignal to obtain the auxiliary data. With this configuration, errors dueto variations of the envelope of the reproduction signal of thewrite-once information can be prevented. In this case, it is preferablethat the second-slice-level setting portion comprises auxiliarylow-frequency component separation means with a time constant that islarger than that of the low-frequency component separation means; areproduction signal reproduced with the optical head or a low-frequencyreproduction signal obtained with the low-frequency component separationmeans is entered into the auxiliary low-frequency component separationmeans; and components with frequencies lower than the low-frequencyreproduction signal are extracted to obtain a second slice level. Withthis configuration, the slice level can be set following the levelvariations of low frequency components, so that the signal easily can bereproduced.

It is preferable that the apparatus for reproducing optical disksaccording to the first configuration further comprises frequencytransformation means for transforming a main information signal includedin a reproduction signal reproduced with the optical head from a timedomain into a frequency domain to produce a first transformation signal;means for producing a mixed signal, wherein auxiliary information hasbeen added or superposed to the first transformation signal; andfrequency inverse-transformation means for transforming the mixed signalfrom the frequency domain to the time domain to produce a secondtransformation signal. With this configuration, the ID signal can bespectrally dispersed, so a deterioration of the video signal, whichcorresponds to the main information, can be prevented, and thereproduction of the main information becomes easier.

In a second configuration of an apparatus for reproducing optical disks,an optical head irradiates linearly polarized light onto an opticaldisk, and a change of a polarization orientation of light that istransmitted or reflected from the optical disk is detected in accordancewith a recording signal on the optical disk. The apparatus comprisesmeans for moving, when necessary, the optical head into a pre-determinedportion of the optical disk where write-once information is stored, andmeans for reproducing the write-once information after detecting achange of a polarization orientation of light that is transmitted orreflected from the pre-determined portion. In accordance with thissecond configuration of an apparatus for reproducing optical disks, thereproduction signal can be detected easily, because it is not influencedby variations of the reflected luminous energy or by noise componentsincluded in the addition signal.

It is preferable that the apparatus for reproducing optical disksaccording to the second configuration further comprises means fordetecting an identifier indicating whether write-once information withincontrol data of the optical disk is present, the indication being basedon a detection signal of detection light that is received with at leastone photo-detector of the optical head or on an addition signal ofdetection signals of detection light that is received with a pluralityof photo-detectors of the optical head, wherein to detect the identifierand to verify whether write-once information is present, the opticalhead is moved to the pre-determined portion of the optical disk wherewrite-once information is stored, when necessary. With thisconfiguration, stripes and defects in the write-once information easilycan be discriminated, so that the start-up time for the apparatus can beconsiderably shortened.

It is preferable that the apparatus for reproducing optical disksaccording to the second configuration further comprises decoding meansfor phase-encoding decoding during reproduction of the write-onceinformation. This configuration can be used for the reproduction ofwrite-once information, such as an ID signal.

In a third configuration of an apparatus for reproducing optical diskswhereon main information is stored and write-once information thatdiffers for each disk is stored, the apparatus comprises a signalreproduction portion for reproducing the main information; a write-onceinformation reproduction portion for reproducing the write-onceinformation; and a watermark attaching portion for producing a watermarksignal based on the write-once information, adding the watermark signalto the main information and giving it out. In accordance with this thirdconfiguration of an apparatus for reproducing optical disks, illegalcopies being made to obtain the main information of, for example, thevideo signal can be prevented.

It is preferable that in the apparatus for reproducing optical disksaccording to the third configuration, the write-once information isrecorded by partially changing a reflection coefficient of a recordinglayer on the optical disk.

It is also preferable that in the apparatus for reproducing opticaldisks according to the third configuration, a recording layer of theoptical disk comprises a magnetic film having a magnetic anisotropy thatis perpendicular to a film surface; and write-once information is storedby partially changing the perpendicular magnetic anisotropy of themagnetic film.

It is also preferable that in the apparatus for reproducing opticaldisks according to the third configuration, a watermark attachingportion overlaps a signal of the main information with auxiliaryinformation comprising a watermark. With this configuration, theauxiliary information being deleted from the main information with anormal recording and reproducing system can be prevented.

It is also preferable that the apparatus for reproducing optical disksaccording to the third configuration further comprises a frequencytransformation means for producing a first transformation signal bytransforming a signal of main information from a time domain into afrequency domain; means for producing a mixed signal by adding orsuperposing write-once information and the first transformation signal;and frequency inverse-transformation means for producing a secondtransformation signal by transforming the mixed signal from thefrequency domain into the time domain.

It is also preferable that the apparatus for reproducing optical disksaccording to the third configuration further comprises an MPEG decoderfor expanding main information into a video signal; and means forinputting the video signal into the watermark attaching portion. Withthis configuration, the watermark can be spectrally dispersed and addedto the main information, such as the video signal, without deterioratingthe signal. In this case, it is preferable that the apparatus furthercomprises a watermark reproduction portion for reproducing watermarks;the MPEG decoder and the watermark reproduction portion both comprise amutual authentication portion; and encrypted main information is sentand decrypted only if the mutual authentication portions authenticateeach other. With. this configuration, illegal elimination ormanipulation of watermarks can be prevented, because the encryption isnot cancelled when the digital signal is intercepted from anintermediate bus. In this case, it is preferable that a compound signalof main information that is compounded with an encryption decoder isinput into the MPEG decoder. With this configuration, there is nocorrelation between information such as the ID and the watermarkproduction parameters, so that illegal copies with unauthorizedwatermarks can be prevented. In this case, it is even more preferablethat the apparatus further comprises a watermark reproduction portionfor reproducing watermarks; an encryption decoder and the watermarkreproduction portion both comprise a mutual authentication portion; andencrypted main information is sent and decrypted only if the mutualauthentication portions authenticate each other.

In a first configuration of an apparatus for recording and reproducingoptical disks whereon information can be recorded, erased and reproducedand whereon main information is stored on a main recording area of arecording layer of the optical disks using a recording circuit and anoptical head, the apparatus comprises means for reproducing write-onceinformation that is recorded onto a pre-determined portion of therecording layer using a signal output portion of the optical head, whichdetects the write-once information as a change of a polarizationorientation; means for recording the main information onto the mainrecording area as encrypted information that is encrypted with anencryption encoder using the write-once information; and means forreproducing the main information by reproducing the write-onceinformation with the signal output portion of the optical head andcomposing the encrypted information as a decryption key in an encryptiondecoder. In accordance with this first configuration of an apparatus forrecording and reproducing optical disks, illegal copies can beprevented, so that the copyright can be protected.

In a second configuration of an apparatus for recording and reproducingoptical disks whereon main information is recorded onto a main recordingarea of a recording layer of the optical disks using a recording circuitand an optical head, the apparatus comprises a watermark attachingportion for adding a watermark to the main information. Write-onceinformation that is stored in a pre-determined portion of the recordinglayer is reproduced with the optical head. The reproduced write-onceinformation is added to the main information as a watermark with thewatermark attaching portion. The main information including thewatermark is recorded onto the main recording area. In accordance withthis second configuration of an apparatus for recording and reproducingoptical disks, the recording history can be traced from the watermarkrecording data, so that illegal copies and illegal use can be prevented.

It is preferable that in the apparatus for recording and reproducingoptical disks according to the second configuration, the maininformation is recorded by partially changing a reflection coefficientof the recording layer.

It is also preferable that in the apparatus for recording andreproducing optical disks according to the second configuration, therecording layer comprises a magnetic film having a magnetic anisotropythat is perpendicular to a film surface; and main information is storedby partially changing a magnetization direction of the magnetic film. Inthis case, it is preferable that the main information and the write-onceinformation are reproduced by detecting a change of a magnetizationorientation of the recording layer or a change of the perpendicularanisotropy of the recording layer with an optical head as a change of apolarization orientation.

It is also preferable that in the apparatus for recording andreproducing optical disks according to the second configuration, awatermark attaching portion overlaps a signal of the main informationwith auxiliary information comprising a watermark.

It is also preferable that the apparatus for recording and reproducingoptical disks according to the second configuration further comprises afrequency transformation means for producing a first transformationsignal by transforming a signal of main information from a time domaininto a frequency domain; means for producing a mixed signal by adding orsuperposing write-once information and the first transformation signal;and frequency inverse-transformation means for producing a secondtransformation signal by transforming the mixed signal from thefrequency domain into the time domain.

It is also preferable that the apparatus for recording and reproducingoptical disks according to the second configuration further comprises anMPEG decoder for expanding main information into a video signal; andmeans for inputting the video signal into the watermark attachingportion. In this case, it is preferable that the apparatus furthercomprises a watermark reproduction portion for reproducing watermarks;the MPEG decoder and the watermark reproduction portion both comprise amutual authentication portion; and encrypted main information is sentand decrypted only if the mutual authentication portions authenticateeach other. It is also preferable that a compound signal of maininformation that is compounded with an encryption decoder is input intothe MPEG decoder. It is even more preferable that the apparatus furthercomprises a watermark reproduction portion for reproducing watermarks;the encryption decoder and the watermark reproduction portion bothcomprise a mutual authentication portion; and encrypted main informationis sent and decrypted only if the mutual authentication portionsauthenticate each other.

In a configuration of an apparatus for recording write-once informationonto an optical disk storing main information, the apparatus comprisesmeans for recording auxiliary information comprising at least one of adisk ID and watermark production parameters. In accordance with thisconfiguration of an apparatus for recording write-once information ontoan optical disk, it can be determined from the disk ID or the watermarkwho made an illegal copy or illegal use of the disk, so that thecopyright can be protected.

It is preferable that in the apparatus for recording write-onceinformation onto an optical disk according to this configuration, themain information is stored by providing convex/concave pits in areflection film of the optical disk, and the auxiliary information isstored by partially erasing the reflection film.

It is also preferable that in the apparatus for recording write-onceinformation onto an optical disk according to this configuration, themain information is stored by partially changing a reflectioncoefficient of a recording layer of the optical disk, and the auxiliaryinformation is stored by partially changing a reflection coefficient ofthe recording layer of the optical disk.

It is also preferable that in the apparatus for recording write-onceinformation onto an optical disk according to this configuration, arecording layer of the optical disk comprises a magnetic film having amagnetic anisotropy that is perpendicular to a film surface; maininformation is stored by partially changing a magnetization direction ofthe magnetic film; and auxiliary information is stored by partiallychanging the perpendicular magnetic anisotropy of the magnetic film.

In a configuration of an apparatus for recording optical disks storingmain information, the apparatus comprises means for producing awatermark based on auxiliary information comprising a disk ID; and meansfor recording data, which consists of certain data to which thewatermark has been superposed. In accordance with this configuration ofan apparatus for recording optical disks storing main information, thewatermark can be detected from the recorded data, and the contentshistory can be determined, so that the copyright can be protected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional drawing showing a configuration of anoptical disk in accordance with an embodiment of the present invention.

FIG. 2 is a cross-sectional drawing showing a configuration of anoptical disk in accordance with another embodiment of the presentinvention.

FIGS. 3(A,B) is a drawing illustrating the principle of howmagneto-optical disks are reproduced in accordance with an embodiment ofthe present invention.

FIG. 4 is a graph showing the Kerr hysteresis loop in a perpendiculardirection to the film surface for a BCA portion that has been heated andfor a non-BCA portion that has not been heated in the recording layer ofthe magneto-optical disk in accordance with an embodiment of the presentinvention.

FIG. 5 is a graph showing the relation between the laser recordingcurrent for recording identifying information on a magneto-optical diskin accordance with the present invention and the BCA recordingcharacteristics.

FIG. 6(a) is a traced graph showing a differential signal waveform of aBCA signal at a recording current of 8A for a magneto-optical disk inaccordance with an embodiment of the present invention. FIG. 6(b) is atraced graph showing its addition signal waveform.

FIG. 7 is a drawing of the optical structure of an apparatus forrecording and reproducing magneto-optical disks in accordance with anembodiment of the present invention.

FIGS. 8(a)-8(f) are process drawings illustrating a method formanufacturing a magneto-optical disk in accordance with an embodiment ofthe present invention.

FIGS. 9(a)-9(c) are process drawings illustrating a method for recordingidentifying write-once information onto a magneto-optical disk inaccordance with an embodiment of the present invention.

FIG. 10 is a drawing showing a apparatus for detecting BCA identifyingwrite-once information from a magneto-optical disk in accordance with anembodiment of the present invention.

FIG. 11(a) is a schematic drawing illustrating the state of the BCAportions when identifying write-once information that has been recordedwith excessive power onto a magneto-optical disk in accordance with anembodiment of the present invention. FIG. 11(b) is a schematic drawingillustrating the state of the BCA portions when identifying write-onceinformation that has been recorded with adequate power onto amagneto-optical disk in accordance with an embodiment of the presentinvention.

FIG. 12(a) is a schematic drawing showing the result of an observationwith an optical microscope and a polarization microscope of a BCAportion when BCA identifying write-once information that has beenrecorded with excessive recording power onto a magneto-optical disk inaccordance with an embodiment of the present invention. FIG. 12(b) is aschematic drawing showing the result of an observation with an opticalmicroscope and a polarization microscope of a BCA portion when BCAidentifying write-once information that has been recorded with adequaterecording power onto a magneto-optical disk in accordance with anembodiment of the present invention.

FIG. 13(a) is a graph showing the rotation angle of the polarizationplane in the non-BCA portions of a magneto-ptical disk in accordancewith an embodiment of the present invention. FIG. 13(b) is a graphshowing the rotation angle of the polarization plane in the BCA portionsof a magneto-optical disk in accordance with an embodiment of thepresent invention.

FIG. 14 is a block diagram of an apparatus for reproducing a DVD-ROM andan apparatus for recording and reproducing a DVD in accordance with anembodiment of the present invention.

FIG. 15 is a block diagram of a stripe recording apparatus in accordancewith an embodiment of the present invention.

FIGS. 16(a)-16(d) are diagrams illustrating the signal waveform and thetrimming for an RZ recording in accordance with an embodiment of thepresent invention.

FIGS. 17(a)-17(e) are diagrams illustrating the signal waveform and thetrimming for a PE-RZ recording in accordance with an embodiment of thepresent invention.

FIG. 18(a) is a perspective drawing of the focusing portion in anembodiment of the present invention. FIG. 18(b) is a drawing showing thestripe arrangement and the emitted pulse signal in an embodiment of thepresent invention.

FIG. 19 is a diagram showing the stripe arrangement on a magneto-opticaldisk in accordance with an embodiment of the present invention, and thecontents of the TOC data.

FIG. 20 is a flowchart illustrating the switching between CAV and CLVfor the stripe reproduction in an embodiment of the present invention.

FIG. 21(a) is a diagram illustrating the data structure after ECCencoding in accordance with an embodiment of the present invention. FIG.21(b) is a diagram illustrating the data structure for n=1 after ECCencoding. FIG. 21(c) is a diagram illustrating the ECC error correctioncapability in an embodiment of the present invention.

FIG. 22(a) is a diagram illustrating the data structure of thesynchronized signal. FIG. 22(b) is a diagram illustrating the waveformof the fixed pattern. FIG. 22(c) is a diagram showing the recordingcapacities.

FIG. 23(a) shows the structure of a low-pass filter. FIG. 23(b) is agraph showing the waveform of a signal after passing through thelow-pass filter.

FIG. 24(a) shows the waveform of the reproduction signal in anembodiment of the present invention. FIG. 24(b) explains the dimensionalaccuracy of the stripes in an embodiment of the present invention.

FIG. 25 is a flowchart showing how the TOC data is read and reproducedin an embodiment of the present invention.

FIG. 26 is a block diagram of the second level slice portion in anembodiment of the present invention.

FIGS. 27(a)-27(d) show the waveform of the reproduction signal atdifferent elements for binarizing the signal in an embodiment of thepresent invention.

FIG. 28 is a block diagram showing a particular circuit structure forthe second level slice portion in an embodiment of the presentinvention.

FIG. 29 is a block diagram showing a circuit structure for the secondlevel slice portion in an embodiment of the present invention.

FIG. 30 is a block diagram showing a circuit structure for the secondlevel slice portion in an embodiment of the present invention.

FIGS. 31(a)-31(d) are diagrams of the actual signal waveform of thereproduction signal at different elements for binarizing the signal inan embodiment of the present invention.

FIG. 32 is a block diagram showing a disk manufacturing apparatus for acontents provider and a reproduction apparatus for a system operator inaccordance with an embodiment of the present invention.

FIG. 33 is a block diagram showing a disk manufacturing portion in adisk manufacturing apparatus in accordance with an embodiment of thepresent invention.

FIG. 34 is a block diagram of an entire broadcasting apparatus and areproduction apparatus on the system operator side in accordance with anembodiment of the present invention.

FIGS. 35(a)-35(h) show graphs of the waveform in the time-domain and thespectrum in the frequency-domain of an original signal and a videosignal in accordance with an embodiment of the present invention.

FIG. 36 is a block diagram of a receiver on the user side and abroadcasting apparatus on the system operator side in accordance with anembodiment of the present invention.

FIG. 37 is a block diagram of a watermark detection apparatus inaccordance with an embodiment of the present invention.

FIGS. 38(a)-38(c) are cross-sectional drawings showing the trimming witha pulsed laser in accordance with an embodiment of the presentinvention.

FIGS. 39(a)-39(g) are diagrams showing the signal reproduction waveformof the trimmed portions in accordance with an embodiment of the presentinvention.

FIG. 40 is a cross-sectional drawing showing the configuration of anoptical disk in accordance with an embodiment of the present invention.

FIG. 41 is a block diagram showing an apparatus for recording andreproducing optical disks in accordance with an embodiment of thepresent invention.

FIG. 42 is a block diagram showing an apparatus for recording andreproducing magneto-optical disks in accordance with an embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a more detailed description of the present invention,with reference to the preferred embodiments.

First Embodiment

First of all, the structure of a magneto-optical disk is explained.

FIG. 1 is a cross-section showing the structure of a magneto-opticaldisk in a first embodiment of the present invention. As is shown in FIG.1, a dielectric layer 212 is formed on top of a disk substrate 211, anda recording layer 213 is formed on top of the dielectric layer 212. Inthe recording layer 213, a plurality of BCA portions 220 a and 220 b(BCA is one of the formats for write-once identification information) isrecorded in a circumferential direction of the disk. On top of therecording layer 213, an intermediate dielectric layer 214 and areflecting layer 215 are deposited in that order. An overcoat layer 216is formed on top of the reflecting layer 215.

Referring to FIG. 8, the following is an explanation of a method forproducing a magneto-optical disk in accordance with this embodiment.

First of all, as shown in FIG. 8(a), a disk substrate 211, which hasguide grooves or prepits for tracking guidance, is produced by injectionmolding using a polycarbonate resin. Then, as is shown in FIG. 8(b), an80 nm thick dielectric layer 212 of SiN is formed on the disk substrate211 by reactive sputtering with a Si target in an atmosphere containingargon gas and nitrogen gas. Then, as is shown in FIG. 8(c), a 30 nmthick recording layer 213 consisting of a TbFeCo film is formed on thedielectric layer 212 by DC sputtering with a TbFeCo alloy target in anargon gas atmosphere. Then, as is shown in FIG. 8(d), a 20 nmintermediate dielectric layer 214 consisting of a SiN film is formed onthe recording layer 213 by reactive sputtering with a Si target in anatmosphere containing argon gas and nitrogen gas. Then, as is shown inFIG. 8(e), a 40 nm thick reflecting layer 215 consisting of an AlTi filmis formed on the intermediate dielectric layer 214 by DC sputtering withan AlTi target in an argon gas atmosphere. Finally, as is shown in FIG.8(f), a 10 μm thick overcoat layer 216 is formed on the reflecting layer215 by dropping an UV-light curing resin on the reflecting layer 215,coating the disk with the UV-light curing resin using a spin-coater at2500 rpm, and curing the UV-light curing resin by irradiating it with UVlight.

The following is an explanation of a method for recording identifyinginformation (write-once information, which is recorded after finishingthe disk manufacturing process), with reference to FIG. 9.

First of all, as is shown in FIG. 9(a), the magnetization orientation ofthe magnetic layer 213 is aligned into one direction with a magnetizer217. The recording layer 213 of the magneto-optical disk of thisembodiment is a vertical magnetization film having a coercive force of11 kOe. Thus, the magnetization orientation of the recording layer 213can be aligned with the direction of the magnetic field generated by themagnetizer 217 by setting the strength of the electric field generatedby the electromagnet of the magnetizer 217 to 15 kGauss, and passing themagneto-optical disk through this magnetic field. Next, as is shown inFIG. 9(b), using a high-power laser 218, for example a YAG laser, and aunidirectional convergence focusing lens 219 such as a cylindrical lens,the laser light is focused on the recording layer 213 in the form ofoblong stripes. BCA portions 220 a and 220 b are recorded as identifyinginformation in the circumferential direction of the disk. The recordingprinciple, recording method and reproduction method are explained inmore detail in the course of this specification. Then, as is shown inFIG. 9(c), a BCA reader 221 is used to detect the BCA portions 220 a and220 b, a PE (phase encode) decoding and a comparison with the recordeddata is performed to verify whether there is a match. If the BCAportions match the recorded data, the recording of the identifyinginformation is completed, and if the BCA portions do not match, themagneto-optical disk is removed from the process.

The following is an explanation of the operation principle of the BCAreader 221, with reference to FIG. 10.

As is shown in FIGS. 10(a) and (c), the BCA reader 221 comprises apolarizer 222 and a detector 223, whose polarizing planes areperpendicular to each other. Consequently, as is shown in FIG. 10(a) and(b), when the laser beam is irradiated at the BCA portion 220 a of therecording layer 213, no detection signal is output, because the verticalmagnetic anisotropy of the BCA portion 220 a is low (the magneticanisotropy in the in-plane direction is dominant). However, when thelaser beam is irradiated at a portion outside the BCA portions (non-BCAportion 224) of the recording layer 213, the polarizing plane of thereflected light rotates and a signal is output to the photo-detector(PD) 256, because this portion is magnetized in a directionperpendicular to the film surface. Thus, a BCA regeneration signal asshown in FIG. 10(b) can be attained, and the BCA portions 220 can bedetected speedily without using an optical head for magneto-opticalrecording and reproduction.

Since the magnetic anisotropy in the vertical direction of the filmsurface of the BCA portions is considerably lower, a BCA reproductionsignal can be attained for the BCA portions 220 a. The following is amore detailed explanation of this:

FIG. 4 shows the hysteresis loop 225 a of a BCA portion 220 of therecording layer 213 that has been heated by irradiation with identifyinginformation, that is, with laser light, and a Kerr hysteresis loop 225 bof a non-BCA portion 224, which has not been heated, in a directionperpendicular to the film plane. It can be seen from FIG. 4, that theKerr rotation angle and the vertical magnetic anisotropy of the heatedBCA portion 220 have been deteriorated considerably. Thus,magnet-optical recording cannot be performed in the heated BCA portions220, because the residual magnetism in the vertical directiondisappears.

As is shown in FIG. 9, in this embodiment, after the magnetizationorientation of the vertical magnetization film in the recording layer213 has been aligned in one direction (that is, after magnetization),the BCA portions 220 are recorded as the identifying information. Afterthe BCA portions 220 have been recorded by layering the layers anddeteriorating the recording layer 213, the magnetization orientation ofthe vertical magnetization film in the recording layer 213 can bealigned into one direction while applying a magnetic field that issmaller than the field that has to be applied at room temperature byirradiating the recording layer 213 with, for example, a stroboscopiclight to raise its temperature.

The recording layer 213 of the magneto-optical disk in the presentembodiment has a coercive force of 11 kOe at room temperature. However,when it is irradiated by, for example, a stroboscopic light or a laserbeam and its temperature is raised to at least 100° C., the coerciveforce becomes about 4 kOe, so that when a magnetic field of at least 5kOe is applied, the magnetization orientation of the recording layer 213can be aligned into one direction.

The following is an explanation of the recording power for amagneto-optical BCA recording.

FIG. 5 shows the BCA recording characteristics for a BCA signal that wasrecorded on a magneto-optical disk using a BCA trimming device (BCArecording device—CWQ pulse recording with a YAG laser excited with a 50W lamp; product by Matsushita Electric Industrial Co., Ltd). As can beseen from FIG. 5, when the recording current of the laser is below 8 A,no BCA portion is recorded. When the recording current of the laser isin the optimal range of 8-9 A, a BCA image 226 a can be attained onlywith a polarization microscope, as is shown in FIGS. 5 and 12(b). ThisBCA image 226 a cannot be observed with an optical microscope. When therecording current of the laser is at least 9 A, the BCA images 226 b and226 c can be attained with both the optical microscope and thepolarization microscope, as is shown in FIGS. 5 and 12(a). When therecording current of the laser as shown in FIG. 5 is higher than 10 A,then the protective layer (overcoat layer) is destroyed. This situationis illustrated in FIG. 11. In FIG. 11, the reflecting layer 215 and theovercoat layer 216 have been destroyed by excessive laser power. On theother hand, when the recording current of the laser is in the optimalrange of 8-9A, only the recording layer 213 is deteriorated as shown inFIG. 11(b), and the reflecting layer 215 and the overcoat layer 216 areleft intact.

The following explains a recording/reproduction apparatus formagneto-optical disks according to this embodiment, with reference toFIG. 7.

FIG. 7 illustrates the optical configuration of a recording/reproductionapparatus for magneto-optical disks according to the first embodiment ofthe present invention. FIG. 7 illustrates an optical head 255 formagneto-optical disks, a pulse generator 254, a laser light source 241,a collimator lens 242, a polarization beam splitter 243, an objectivelens 244 for focusing the laser beam on the magneto-optical disk, a halfmirror 246 for separating the light reflected from the magneto-opticaldisk into a signal reproduction direction and a focus tracking controldirection, a λ/4-plate 247 for rotating the polarization plane of thelight reflected from the magneto-optical disk, a polarization beamsplitter 248 for separating the light reflected from the magneto-opticaldisk according to its polarization plane, photo-detectors 249 and 250,and a receiver/controller 253 for focus tracking. Further indicated area magneto-optical disk according to the present embodiment, a magnetichead 251, and a magnetic head modulation driving circuit 252.

As is shown in FIG. 7, a linearly polarized laser beam emitted from thelaser light source 241 is collimated by the collimator lens 242 into aparallel laser beam. Only the P-polarized component of this parallellaser beam passes the polarization beam splitter 243, is focused by theobjective lens 244 and irradiated onto the recording layer of themagneto-optical disk 240. Thus, the information concerning the regularrecording data (data information) is recorded by partially changing themagnetization orientation of the vertical magnetization film (pointingupwards and downwards). Owing to the magneto-optical effect, theorientation of the polarization plane of the light that is reflected (ortransmitted) by the magneto-optical disk 240 changes according to themagnetization. The reflected light, whose polarization plane was thusrotated, is irradiated on the polarization beam splitter 243, and thenseparated by the half mirror 246 into a signal reproduction directionand a focus tracking control direction. The polarization plane of thebeam of the signal reproduction direction is rotated 45° by a λ/4 plate.Then, the P-polarized component and the Spolarized component areseparated by the polarization beam splitter 248. The light is thusseparated into two light beams, whose luminous energy is detected by thephoto-detectors 249 and 250. A change in the orientation of thepolarization plane is detected as a differential signal of the luminousenergies detected by the two photo-detectors 249 and 250. Thereproduction signal for the data information is obtained from thisdifferential signal. The focus tracking controller 253 uses the lightthat has been separated by the half mirror 246 into the focus trackingcontrol direction to control the focus of the objective lens 244 and tocontrol tracking.

The BCA portions 220, serving as identifying information for themagneto-optical disk in his embodiment, are detected with the samereproduction method as the data information. As is shown in FIG. 4, thevertical magnetic anisotropy of the heated BCA portions 220 deterioratesconsiderably (hysteresis loop 225 a). When the recording layer isproduced or when the signal is reproduced, the magnetization directionof the vertical magnetization layer is aligned in one direction, so thatthe polarization plane of a laser beam that is irradiated on the notheated non-BCA portions 224 with greater vertical magnetic anisotropy isrotated for an angle θ_(k) in accordance with the magnetizationdirection. On the other hand, the Kerr rotation angle of the BCAportions 220, which have been heated and whose vertical magneticanisotropy is considerably deteriorated, has become very small, so thatthe polarization plane of a laser beam that is irradiated on the BCAportions 220 hardly rotates at all when reflecting the laser beam.

The following is a method for aligning the magnetization direction ofthe vertical magnetization film into one direction, when the BCAportions are reproduced: A magneto-optical disk recording/reproductionapparatus as shown in FIG. 7 irradiates a laser beam of at least 4 mWonto the magnetic layer 213 of a magneto-optical disk 240, so that themagnetic layer 213 is heated to at least the Curie temperature. At thesame time, the magnetic head 251 applies a constant magnetic field of atleast 200 Oe, so that the magnetization direction of the recording layerof the BCA portions is aligned into one direction.

FIG. 6(a) shows an actual traced waveform of the detected differentialsignal for the identifying data. FIG. 6(b) shows a traced waveform ofthe detected all-sum signal of the identifying signal, which is asummation signal detected with several photo-detectors. As can be seenfrom FIG. 6(a), the identifying information can be detected as a pulsewaveform with a sufficient amplitude ratio in the differential signal.Even when the magnetic properties of the recording layer change or aportion of the recording layer is crystallized, the change of theaverage refractive index will be less than 5%, so that the variations inthe luminous energy of the light reflected from the magneto-optical diskare less than 10%. Consequently, the variations of the reproductionwaveform caused by a change of the luminous energy of the reflectedlight are very small.

FIG. 13 illustrates the polarization of the reflected light compared tothat of the incident light. As is shown in FIG. 13(b), light reflectingfrom the heated BCA portions 220 has exactly the same polarizationdirection 227 b as incident light. On the other hand, light reflectingfrom the non-BCA portions 224 has a polarization direction 227 a that,owing to the Kerr effect in the magnetization film having with verticalmagnetization anisotropy, is rotated by a rotation angle θ_(k) againstthe polarization direction of the incident light.

Moreover, this embodiment detects the identifying information from adifferential signal. Using this reproduction method, variations of theluminous energy that do not follow the polarized light can be almostcompletely canceled, so that the noise due to these luminous energyvariations can be reduced.

Second Embodiment

FIG. 2 is a cross-section showing the structure of a magneto-opticaldisk in a second embodiment of the present invention. As is shown inFIG. 2, a dielectric layer 232 is formed on top of a disk substrate 231,and a tri-layer recording layer comprising a magnetic reproduction film233, an intermediate magnetic film 234, and a magnetic recording film235 is formed on top of the dielectric layer 232. In the recordinglayer, a plurality of BCA portions 220 a and 220 b is recorded in acircumferential direction of the disk. On top of the recording layer, anintermediate dielectric layer 236 and a reflecting layer 237 aredeposited in that order. An overcoat layer 238 is formed on top of thereflecting layer 237.

Referring to FIG. 8 of the first embodiment and to FIG. 9, the followingis an explanation of a method for producing a magneto-optical disk inaccordance with this embodiment.

First of all, a disk substrate 231, which has guide grooves or pre-pitsfor tracking guidance, is produced by injection molding using apolycarbonate resin. Then, an 80 nm thick dielectric layer 232 of SiN isformed on the disk substrate 231 by reactive sputtering with a Si targetin an atmosphere containing argon gas and nitrogen gas. The recordinglayer comprises a magnetic reproduction film 233 of GdFeCo with a Curietemperature of T_(c1) and a coercive force of H_(c1), an intermediatemagnetic film 234 of TbFe with a Curie temperature of T_(c2) and acoercive force of H_(c2), and a magnetic recording film 235 of TbFeCowith a Curie temperature of T_(c3) and a coercive force of H_(c3). Thesefilms are formed on top of the dielectric layer 232 by DC sputteringwith alloy targets in an Ar gas atmosphere. Then, a 20 nm intermediatedielectric layer 236 consisting of a SiN film is formed on the recordinglayer by reactive sputtering with a Si target in an atmospherecontaining argon gas and nitrogen gas. Then, a 40 nm thick reflectinglayer 237 consisting of an AlTi film is formed on the intermediatedielectric layer 236 by DC sputtering with an AlTi target in an argongas atmosphere. Finally, an 8 μm thick overcoat layer 238 is formed onthe reflecting layer 237 by dropping an UV-light curing resin on thereflecting layer 237, coating the disk with the UV-light curing resinusing a spin-coater at 3000 rpm, and curing the UV-light curing resin byirradiating it with UV light.

The reproduction magnetic layer 233 is set to a thickness of 40 nm, aCurie temperature T_(c1) of 300° C., and a coercive force H_(c1) of 100Oe at room temperature. The intermediate magnetic film 234 is set to athickness of 10 nm, a Curie temperature T_(c2) of 120° C., and acoercive force H_(c2) of 3 kOe at room temperature. The magneticrecording film 235 is set to a thickness of 50 nm, a Curie temperatureT_(c3) of 230° C., and a coercive force H_(c3) of 15 kOe at roomtemperature.

The following explains the reproduction principle for the tri-layerrecording layer of this embodiment with reference to FIG. 3. FIG. 3shows a reproduction magnetic field 228, laser light spots 229 a, 229 b,and 229 c, recording domains 230, a magnetic reproduction film 233, anintermediate magnetic film 234, and a magnetic recording film 235. As isshown in FIG. 3, the domains 230 containing the information signals arerecorded into the magnetic recording film 235. At room temperature, themagnetization of the magnetic recording film 235 is transferred to themagnetic reproduction film by coupling forces between the magneticrecording film 235, the intermediate magnetic film 234, and the magneticreproduction film 233.

At signal reproduction, the regeneration magnetic film 233 retains thesignal of the magnetic recording film 235 in the low temperature portion229 b of the laser beam spot 229 a. In the high temperature portion 229c of the laser beam spot 229 a, however, the temperature of theintermediate magnetic film 234 rises above the Curie temperature, sothat the coupling forces between the recording magnetic layer 235 andthe reproduction magnetic layer 233 are interrupted and themagnetization direction of the magnetic reproduction film 233 is alignedwith the magnetization direction of the magnetic reproduction film 228,because the Curie temperature of the intermediate magnetic film 234 islower than that of the other magnetic films. Therefore, the recordingdomains 230 become masked by the high temperature portion 229 c, whichis a part of the laser beam spot 229 a. Consequently, the signal can bereproduced only from the low temperature portion 229 b of the laser beamspot 229 a. This reproduction method is a magnetically induced superresolution method called “FAD”. Using this reproduction method, a signalreproduction with regions smaller than the laser beam spot becomespossible.

A similar reproduction is also possible when the magnetically inducedsuper resolution method called “RAD” is used, wherein signalreproduction is possible only in the high temperature portion of thelaser beam spot.

The following explains the recording method for identifying information(write-once information) in a magneto-optical disk of this embodiment,with reference to FIG. 9.

First of all, as is shown in FIG. 9(a), the magnetization orientation ofthe recording layer is aligned into one direction with the magnetizer217. The magnetic recording film 235 of the recording layer in themagneto-optical disk of this embodiment is a vertical magnetization filmhaving a coercive force of 15 kOe. Thus, the magnetization orientationof the recording layer can be aligned with the direction of the magneticfield generated by the magnetizer 217 by setting the strength of theelectric field generated by the electromagnet of the magnetizer 217 to20 kGauss, and passing the magneto-optical disk through this magneticfield. Next, as is shown in FIG. 9(b), using a high-power laser 218, forexample a YAG laser, and a unidirectional convergence focusing lens 219such as a cylindrical lens, the laser light, is focused on the recordinglayer in form of oblong stripes. BCA portions 220 a and 220 b arerecorded in the circumferential direction of the disk. The recordingprinciple, recording method and reproduction method are the same as inthe first embodiment. As in the first embodiment, the recording layeralso can be magnetized after the BCA recording. When the temperature ofthe recording layer is raised for magnetization using, for example, astroboscopic light, the magnetization orientation of the recording layeralso can be aligned into one direction with a magnetic field that is assmall as 5 kOe.

BCA portions 220 a and 220 b are recorded in the circumferentialdirection of the disk. The recording principle, recording method andreproduction method are the same as in the first embodiment. As in thefirst embodiment, the recording layer also can be magnetized after theBCA recording. When the temperature of the recording layer is raised formagnetization using, for example, a stroboscopic light, themagnetization orientation of the recording layer also can be alignedinto one direction with a magnetic field that is as small as 5 kOe.

The recording layer of this embodiment is a tri-layer and comprises themagnetic reproduction film 233, the intermediate magnetic film 234, andthe magnetic recording film 235, The identifying information can berecorded by considerably decreasing the magnetic anisotropy in adirection perpendicular to the film surface in at least the portionwhere the magnetic recording film 235 has been heated, and letting themagnetic anisotropy in substantially in-plane directions dominate.

The Curie temperature and the coercive force of the magnetic filmconstituting the recording layer can be changed relatively easily bychoosing a material with different structure or by adding atoms withdifferent vertical magnetic anisotropy. Therefore, the conditions forproducing the recording layer of the magneto-optical disk and theconditions for recording the identifying information can be optimallyset.

In the first and second embodiments, a polycarbonate resin is used forthe disk substrates 211 and 231, a SiN film is used for the dielectriclayers 212, 214, 232, and 236, and a TbFeCo film, a GdFeCo film, and aTbFe film are used for the magnetic films. However, it is also possibleto use glass or plastic, such as a polyolefin or PMMA, for the disksubstrates 211 and 231. It is also possible to use other nitride filmssuch as AlN, or oxide films such as TaO₂, or chalcogen composition filmssuch as ZnS, or a film of a mixture of at least two of the above for thedielectric layers 212, 214, 232, and 236. It is also possible to userare earth metal—transition metal ferrimagnetic film of a differentmaterial or structure, or a MnBi film, PtCo film or any other magneticfilm with vertical magnetic anisotropy for the magnetic film.

Moreover, In the second embodiment, the vertical magnetic anisotropy ofthe magnetic recording film 235 in the tri-layer recording layer wasdeteriorated. However, the same effect can be attained when the verticalmagnetic anisotropy of either the magnetic reproduction film 233 or themagnetic recording film, or both, or the vertical magnetic anisotropy ofthe magnetic reproduction film 233, the intermediate magnetic film 234,and the magnetic recording film 235 is deteriorated.

Third Embodiment

FIG. 40 is a cross-section showing the structure of a magneto-opticaldisk in a third embodiment of the present invention. As is shown in FIG.40, a dielectric layer 302 is formed on top of a disk substrate 301, anda recording layer 303 of a phase-changeable material that can reversiblychange between a crystal phase and an amorphous phase is formed on topof the dielectric layer 302. In the recording layer 303, a plurality ofBCA portions 310 is recorded in a circumferential direction of the disk.On top of the recording layer 303, an intermediate dielectric layer 304and a reflecting layer 305 are deposited in that order. An overcoatlayer 306 is formed on top of the reflecting layer 305. Two opticaldisks, of which only the first disk has the overcoat layer 306 arelaminated by adhesion layer 307. It is also possible to laminatetogether two optical disks of the same configuration by hot-melting.

The following is an explanation of a method for producing amagneto-optical disk in accordance with this embodiment.

First of all, a disk substrate 301, which has guide grooves or pre-pitsfor tracking guidance, is produced by injection molding using apolycarbonate resin. Then, an 80 nm thick dielectric layer 302 ofZnSSiO₂ is formed on the disk substrate 301 by high-frequency RFsputtering with a ZnSSiO₂ target in an atmosphere containing argon gas.Then, a 20 nm recording layer 303 of a GeSbTe alloy is formed on top ofthe dielectric layer 302 by RF sputtering with a GeSbTe alloy in an Argas atmosphere. Then, a 60 nm intermediate dielectric layer 304consisting of a ZnSSiO₂ film is formed on the recording layer 303 by RFsputtering with a ZnSSiO₂ target in an atmosphere containing argon gas.Then, a 40 nm thick reflecting layer 305 consisting of an AlCr film isformed on the intermediate dielectric layer 304 by DC sputtering with anAlCr target in an argon gas atmosphere. Then, a 5 μm thick overcoatlayer 306 is formed on the reflecting layer 305 by dropping an UV-lightcuring resin on the reflecting layer 305, coating the disk with theUV-light curing resin using a spin-coater at 3000 rpm, and curing theUV-light curing resin by irradiating it with UV light. Thus, a firstoptical disk is obtained. Similarly, a second optical disk is obtained,but without forming the overcoat layer. Finally, the first and thesecond optical disks are laminated to each other by hot-melting, andcuring an adhesive that forms an adhesive layer 307.

The recording of information on the recording layer 303 of the GeSbTealloy uses local changes in the portions where laser light is focused ona microscopic spot. In other words, the difference of the opticalproperties between the crystal phase and the amorphous phase, which arebased on reversible structural changes on the atomic level, are used.The recorded information can be reproduced by detecting the differenceof the reflected luminous energy or the transmitted luminous energy at acertain wavelength.

When an optical disk has a recording layer consisting of a thin filmthat can be reversibly changed between these two optically detectablestates, it can be used as a high-density rewritable exchangeable medium,for example a DVD-RAM.

The recording method for identifying information (write-onceinformation) according to this embodiment can be almost the same as inthe first and the second embodiment. That is, using a high-power laser,for example a YAG laser, and a unidirectional convergence focusing lenssuch as a cylindrical lens, a laser beam is focused on the recordinglayer 303 as oblong stripes. BCA portions 310 are recorded in thecircumferential direction of the disk. When a laser beam with higherpower than for the recording of information in the recording layer 303is irradiated on the optical disk of this embodiment, an excessivestructural change due to crystallization by phase transition occurs.Thus, it becomes possible to non-reversibly record the BCA portions 310.It is preferable that the BCA portions 310 are recorded asnon-reversible crystal phases. By thusly recording the BCA portions 310(i.e. the identifying information) the luminous energy reflected fromthe portions where identifying information is recorded differs from theluminous energy reflected from other portions. Therefore, as in thefirst embodiment, the identifying information can be reproduced with anoptical head. It is preferable that the difference of the luminousenergies reflected from the optical disk is at least 10%. By setting thedifference of the average refractive indices to at least 5%, the changeof the reflected luminous energies can be set to at least 10%. In thecase of DVD-RAMs, as in the case of DVD-ROMs, not only an excessivestructural change of the recording layer can be brought about, but it isalso possible to raise the difference of the reflected luminous energiesabove a certain value by partially destroying the protective layer orthe reflecting layer to reproduce the BCA signal. Moreover, since it isa laminated structure, there are no problems with reliability.

The following explains an apparatus and a method for recordingidentifying information (write-once information) in accordance with thepresent invention with reference to the drawings.

Since the identifying information is compatible with diskrecording/reproduction apparatuses for DVDs, the technology forrecording identifying information on a DVD and the format of therecorded signal is explained in more detail, whereas explanations on thereproduction signal pattern of the magneto-optical disk are omitted.However, since the identifying information in a high-densitymagneto-optical disk such as an ASMO (Advanced Stage Magneto-OpticalDisk) is performed with an optical head 255 as shown in FIG. 7, and thereproduction conditions are different from the detection method of therecording signal.

FIG. 15 is a block diagram of a laser recording apparatus according toan embodiment of the present invention. FIG. 16 illustrates the signalwaveform and trimming shape of an “RZ recording” in an embodiment of thepresent invention. As is shown in FIG. 16(a), the present invention usesan RZ recording for the identifying information. In an RZ recording, onetime unit is divided into several timeslots, for example a firsttimeslot 920 a, a second timeslot 921 a, a third timeslot 922 a, etc.When the data is “00”, a pulse 924 a whose width is narrower than thetimeslot period (that is, the period T of the channel clock) in thefirst timeslot 920 a (that is, between t=t1 and t=t2), as shown in FIG.16(a). Influences of rotational instabilities of the motor 915 shown inFIG. 15 can be removed by letting a clock signal generator 913 generatethe clock signal in accordance with a rotational pulse from a rotationsensor 915 a of the motor 915, and synchronizing the recordingtherewith. The stripe 923 a in the first recording area 925 a of thefour recording areas on the disk, which indicates a “00”, is trimmedwith the laser, as is shown in 16(b).

When the data is “01”, a pulse 924 b whose width is narrower than thetimeslot period (that is, the period T of the channel clock) is recordedin the second timeslot 921 b (that is, between t=t2 and t=t3), as shownin FIG. 16(c). The stripe 923 b in the second recording area 926 b ofthe four recording areas on the disk, which indicates a “01”, is trimmedby the laser, as is shown in 16(d).

A “10” and a “11” are recorded in the third timeslot 922 a and thefourth timeslot, respectively.

Thus, a circumferential barcode as shown in FIG. 39(a) is recorded onthe disk.

The following explains the “NRZ recording” used in a conventionalbarcode recording. In a NRZ recording, a pulse with the same width asthe timeslot period (that is, the period T of the channel clock) isrecorded. In the RZ recording of the present invention, (1/n) T issufficient for the pulse width of one pulse, but for a NRZ recording, abroader width T is necessary for the pulse width. When several Ts followupon each other, a double or triple pulse width of 2T or 3T becomesnecessary.

With laser trimming as in the present invention, it is necessary tochange the configuration of the apparatus itself to change the linewidth for laser trimming, which is difficult to realize and notpractical for NRZ recording. Consequently, to represent a “00”, stripesof the temporal width T are formed in the first and third recording areataken from the left, and to represent a “10”, a stripe of the temporalwidth 2T is formed in the second and third recording area taken from theleft.

In conventional NRZ recording, the pulse width is 1T or 2T, so that itis clear that the laser trimming of the present invention is notapplicable. The stripes (barcode) recorded by the laser trimming of thepresent invention are reproduced as shown in FIG. 6(a) or FIG. 31(a),which show experimental results. However, the trimming line width variesfrom disk to disk, so that a precise control is very difficult. Thereason for this is that when the reflecting film or the recording layerof the optical disk is trimmed, the trimming line width varies owing tovariations of the pulse laser output power, thickness and material ofthe reflecting layer, and thermal conductivity and thickness of the disksubstrate. Moreover, when barcodes with different line widths areprovided on the same disk, the structure of the recording apparatusbecomes complicated. For example, for an NRZ recording used for aproduct barcode, the trimming line width has to be matched precisely tothe channel clock period, that is 1T, 2T, 3T or, generally speaking, nT.It is particularly difficult to change the line widths between 2T, 3Tetc. while recording the bars. The barcode format for conventionalproducts is NRZ, so that when it is applied to the laser barcode of thepresent invention, it is difficult to precisely record different linewidths of 2T, 3T etc. on the same disk, which decreases the yield.Moreover, since the laser trimming line width varies, a stable recordingcannot be achieved and decoding becomes difficult. By using RZ recordingas in the present invention, a stable digital recording can be achieved,even when the laser trimming line width varies. Moreover, there has tobe only one laser trimming line width for RZ recording, so that it isnot necessary to modulate the laser power and the structure of therecording apparatus can be simple.

The following explains the PE modulation of an RZ recording. FIG. 17shows the signal waveform and trimming form of the PE-modulated RZrecording in FIG. 16. First of all, if the data is “0”, a pulse 924 awith a temporal width that is smaller than the time slot period (that isthe channel clock period T) is recorded in the left timeslot 920 a (thatis between t=t1 and t=t2) of the two timeslots 920 a and 921 a, as shownin FIG. 17(a). If the data is “1”, a pulse 924 b with a temporal widththat is smaller than the time slot period (that is the channel clockperiod T) is recorded in the right timeslot 921 b (that is between t=t2and t=t3) of the two timeslots 920 b and 921 b, as shown in FIG. 17(c).A stripe 923 a indicating a “0” is recorded in the left recording area925 a, and a stripe 923 b indicating a “1” is recorded in the rightrecording area 926 b by laser trimming, as shown in FIGS. 17(b) and17(d) [(2) and (4)]. Thus, in the case of a “010”, a pulse 924 c isrecorded in the left timeslot (to represent “0”), a pulse 924 d isrecorded in the right timeslot (to represent “1”), and a pulse 924 e isrecorded in the left timeslot (to represent “0”), as shown in FIG.17(e). The stripes are trimmed by a laser in the left, the right andagain the left recording areas of two recording areas each on the disk.FIG. 17(e) shows the signal for the PE-modulated data “010”. As is shownin FIG. 17(e), there is a signal for each channel bit. In other words,the signal density is usually constant and DC-free. Since this PEmodulation is DC-free, it is robust against low-frequency components,even when the pulse edge is detected at reproduction time. Consequently,the decoding circuit for the disk reproduction apparatus can be simpler.Moreover, since there is at least one pulse 924 within a channel clocktime of 2T, a clock that is synchronized with the channel clock can bereproduced without using a PLL.

In this manner, a circular barcode as shown in FIG. 39(a) is recorded onthe disk. To record the data “01000” of FIG. 39(d) with the PE-RZrecording of this embodiment, a barcode 923 corresponding to therecording signal 924 of FIG. 39(c) is recorded as shown in FIG. 39(b).When the optical pickup of the reproduction apparatus reproduces thisbarcode, a reproduction signal with a waveform as shown in FIG. 39(e) isattained, because the reflection signal in a portion of the pitmodulation signal is lost due to defective portions in the reflectinglayer of the barcode. After passing the regeneration signal through asecond-order or third-order Tchebychev LPF 943 as shown in FIG. 23(a), asignal with the waveform shown in FIG. 39(f) is attained. This signal issliced with a level slice portion, and the reproduction data “01000”shown in FIG. 39(g) is reconstructed.

As is explained with FIGS. 11(a) and (b), when laser trimming withexcessive power is performed on a single-substrate magneto-optical disk,the overcoat layer (protective layer) is destroyed. Consequently, afterlaser trimming was performed with excessive power, it is necessary toreform the protective layer at the factory. Therefore, barcode recordingcannot be performed at software companies or retailers, so that itsapplication will be very limited. It is also possible that there will beproblems with its reliability.

Laser trimming recordings of write-once information on single-substratemagneto-optical disks without destroying the overcoat layer (protectivelayer) can be achieved by heating only the recording layer and changingthe magnetic anisotropy in the direction perpendicular to the filmsurface. When this was experimentally verified, there was no change inthe magnetic properties after 96 hours at 85° C. and 95% humidity.

On the other hand, when the laser trimming recording method of thepresent invention was applied to a laminated disk of two optical diskswith transparent substrates, the protective layer remains without beingdestroyed, which was experimentally verified with a ×800 opticalmicroscope. Also in a similar experiment with a magneto-optical disklasting 96 hours at 85° C. and 95% humidity, no change in the reflectionfilm at the trimmed portions could be observed. Thus, by applying thelaser trimming recording method of the present invention to laminateddisks, such as DVDs, the protective layer does not have to be reformedat the factory, so that a barcode laser trimming recording can beperformed at places other than the press factory, for example, atsoftware companies or at retailers. Therefore, it is not necessaryanymore to give secret keys of software company codes to anyone outsidethe company, so when security information, such as a serial number forcopy protection, is recorded in the barcode, its security can be greatlyimproved. As will be explained further below, by setting the trimmingline width for DVDs to 14T (that is, 1.82 μm), the barcode can beseparated from the pit signals of the DVD, so that the barcode can berecorded superimposed on the pit recording areas of the DVD. Thus, byapplying the trimming method and the modulation recording method of thepresent invention to a laminated disk, such as a DVD, a secondaryrecording can be performed after shipping from the factory. A secondaryrecording also can be performed by applying the same recording method tomagneto-optical disks.

The following explains the operation of the laser recording apparatuswith reference to FIG. 15. As is shown in FIG. 15, first, the entereddata is merged with an ID number issued by a serial number generator 908in an input portion 909. An encryption encoder 830 signs or encryptswith an encryption function such as RSA or DES, as necessary. An ECCencoder 907 performs error correction encoding and adds interleaf. Then,a PE-RZ modulation is performed with a PE-RZ modulator 910. A clocksignal generator 913 generates the modulation clock by synchronizing therotation pulse from a motor 915 or a rotation sensor 915 a. Based on thePE-RZ modulation signal, a laser emission circuit 911 generates atrigger pulse. This trigger pulse is input into a high-power laser 912,for example a YAG laser, driven by a laser power circuit 929. Thereby,pulsed laser light is emitted, which is focused by a focusing member 914on the recording layer 235 of a single-substrate magneto-optical disk240, or on the recording layer 303 of a laminated disk 300, or on thereflecting film 802 of a laminated disk 800. This produces abarcode-shaped deterioration recording or erasure of the recordinglayers 235, 303 or the reflecting film 802. Error correction techniqueswill be explained in more detail further below. The adopted encryptionmethod is to sign the private key of the software company used by thepublic key code as the serial number. Doing so, nobody but the softwarecompany has the private key, and since it is not possible to come upwith a new serial number, the unlawful issuance of serial numbers byparties other than the software company can be prevented. Also, sincethe public key cannot be read “backwards” the security of the system ishigh. Thus, even when the public key is recorded on the disk andtransmitted with the reproduction apparatus, counterfeiting can beprevented. The magneto-optical disk 240, the DVD-RAM disk 300 and theDVD-ROM disk 800 are discriminated by the disk discriminator 260, whichuses the reflection coefficient and a means for reading the disk-typeidentifying information. In the case of a magneto-optical disk 240, therecording power is lowered and the lens is defocused. Thus, a stable BCArecording can be recorded on the magneto-optical disk 240.

The following paragraph explains the focusing member 914 of the laserrecording apparatus with reference to FIG. 18.

As is shown in FIG. 18(a), the light from the laser 912 enters afocusing member 914, and is collimated by a collimator 912 a. Acylindrical lens 917 focuses the laser light only in the circumferentialdirection on the optical disk, so that the light turns into a stripeextending in the radial direction. A mask 918 trims this light, and afocusing lens 919 focuses the light on the recording layer 235 of themagneto-optical disk 240, or the recording layer 303 of the DVD-RAM disk300, or the reflection film 802 of the DVD-ROM disk 800. The recordinglayers 235, 303 or the reflection film 802 are deterioration-recorded orerased in stripe-form. The mask 918 controls the four sides of thestripe. However, in reality, it is sufficient if only one peripheralside in the longitudinal direction of the stripe is controlled. Thus, astripe 923 as shown in FIG. 18(b) can be recorded on the disk. In PEmodulations, the three stripe intervals 1T, 2T and 3T are possible.Discrepancies from these intervals cause jitter, which brings the errorrate up. Since in the present invention the clock generator 913generates the recording clock in sync with the rotation pulse from themotor 915, and passes it on to the modulator 910, the stripes 923 can berecorded precisely in accordance with the motor 915, or in other words,with the rotation of the magneto-optical disk 240, the DVD-RAM disk 300,or the DVD-ROM disk 800. Therefore, jitter can be reduced. It is alsopossible to scan a continuously excited laser in a radial direction andform a barcode using a scanning means for the laser.

FIG. 19 illustrates the characteristics of the disk format. As is shownin FIG. 19, on a DVD, all data are recorded with CLV. However, thestripes 923 of the present invention are recorded by CAV, overlappingthe prepit signals of the read-in data areas (overlap-writing), whichare recorded with CLV. Thus, the CLV data are recorded by a pit patternon the master record, whereas the CAV data are recorded by deleting thereflective film off with the laser. Because of this overlap-writing,pits are recorded between 1T, 2T, and 3T of the barcode stripes. Usingthis pit information, tracking with an optical head becomes possible,and T_(max) and T_(min) of the pit signal can be detected. Thus, therotation speed of the motor can be controlled by detecting thesesignals. If the relation between the trimming width t of the stripes andthe pit clock T(pit) is t>14T(pit), T_(min) can be detected, and therotation speed of the motor can be controlled by detecting this signal.If t is shorter than 14T(pit), its pulse width becomes the same, and itis impossible to discern the stripes 923 a and the pits, so thatdecoding becomes impossible. Moreover, since the address information ofthe pits is read at the same radial position as the stripes, the addressinformation can be obtained and track jumping performed, because thelength of the address region 944 contains at least one frame of pitinformation. Moreover, as is shown in FIG. 24, by providing a ratio,i.e. a duty ratio, between stripes and non-stripes of less than 50%,that means T(S)<T(NS), the substantial reflection coefficient only drops6 dB so that the focus of the optical head can be applied steadily.There are players that cannot control tracking due to the stripes, butsince the stripes 923 are CAV data, reproduction by optical pickup ispossible, if driving is performed using a rotation pulse from, forexample, a Hall element of the motor 17 and CAV rotation.

In magneto-optical disks, the variation of the reflection coefficient isless than 10%, so that it has absolutely no influence on the focuscontrol.

FIG. 20 is a flowchart showing the order of operations when the pit dataof the optical tracks in the stripe area are not reproduced correctly.When the optical disk is inserted (step 930 a), first the optical headis moved to the inner perimeter of the optical disk (step 930 b) andaccesses the stripes 923 shown in FIG. 19. When the pit signals in thearea of the stripes 923 are not all correctly reproduced, the rotationalphase control for CLV cannot be applied. Therefore, rotation speedcontrol is applied by measuring the frequency or T_(max) or T_(min) ofthe pit signals with a rotation sensor of the hole element of the motor(step 930 c). Then, it is determined whether there are stripes or not(step 930 i). If there are no stripes the optical head moves to theouter perimeter of the optical disk (step 930 f). If there are stripes,the stripes (barcode) are reproduced (step 930 d). Then, it isdetermined whether the reproduction of the barcodes is finished (step930 e). If the reproduction of the barcodes is finished, the opticalhead moves to the outer perimeter of the disk (step 930 f). Since thereare no stripes in this area, the pit signals are completely reproducedand the focus and tracking servo are applied correctly. Moreover, sincethe pit signals are completely reproduced in this manner, a regularcontrol of the rotation phase becomes possible (step 930 g) and CLVrotation is possible. Therefore, the pit signal can be correctlyreproduced in step 930 h.

Thus, by switching between rotation speed control and rotation phasecontrol, two different types of data, namely data of stripes (barcodes)and data recorded in pits, can be reproduced. Because the stripes(barcodes) are at the innermost perimeter of the optical disk, it ispossible to switch between the two kinds of rotation control, i.e.rotation speed control and rotation phase control, by measuring theposition of the optical head in the radial direction of the disk usingan optical head stopper and the address information of the pit signals.

The format for high-speed switch recording is illustrated by the datastructure for synchronized encoded data in FIG. 22.

The fixed pattern in FIG. 22(a) is “01000110”. Usually, a pattern suchas “01000111” with the same number 0's and 1's is normal for a fixedpattern, but in the present invention, the data rather has thisstructure. The reason for this is as follows: To perform high-speedswitch recording, at least two pulses have to fit into 1t. Since thedata area is a PE-RZ recording as shown in FIG. 21(a), high-speed switchrecording is possible. However, the synchronized coding in FIG. 22(a) isarranged as irregular channel bits, so that in regular methods there maybe two pulses within 1t, in which case high-speed switch recordingcannot be performed. In the present invention, the fixed pattern is forexample “01000110”. Consequently, as is shown in FIG. 22(b), there isone pulse on the right side of T₁, no pulse in T₂, one pulse on theright side of T₃, and one pulse on the left side of T₄, and there is notimeslot with two pulses. Therefore, by adopting synchronized coding inthe present invention, high-speed switch recording becomes possible, andthe production speed can be doubled.

The following is an explanation of a recording/reproduction apparatus.FIG. 14 is a block diagram of a recording/reproduction apparatus. Thefollowing explanation concentrates on decoding. A low-pass filter 943eliminates high-frequency components due to the pits from the stripesignal output. In case of a DVD, the signal of a maximum of 14T withT=0.13 μm may be reproduced. In this case, high-frequency components canbe eliminated by passing the signal through a second-order orthird-order Tchebychev low-pass filter 943 as shown in FIG. 23(a), aswas experimentally verified. In other words, if a low-pass filter of atleast second order is used, the pit signal and the barcode signal can bedifferentiated, and the barcode can be reliably reproduced. FIG. 23(b)shows the waveform for a worst-case simulation.

Thus by using a low-pass filter 943 of at least second order, the pitregeneration signal can be eliminated almost completely, and the striperegeneration signal can be output, so that the strip signal can bereliably decoded.

Returning to FIG. 14, a PE-RZ decoder 930 a decodes the digital data,and this data is error-corrected by an ECC decoder 930 b. Then, adeinterleaving portion 930 d cancels the interleaf, and an RS decoder930 c performs the calculations for decoding the Reed-Solomon coding, toperform error correction. As is shown by the data structure in FIG.21(a), the interleaf and the Reed-Solomon error correction encoding areperformed with an ECC encoder 907, as shown in FIG. 15. Consequently, byadopting this data structure, if the byte error rate before correctionis 10⁻⁴, a disk error will occur in only one out of 10⁷ disks, as isshown in FIG. 21(c). As is shown in FIG. 22(a), in this data structure,one sync code is assigned for every four synchronized encodings toreduce the data length of the code, whereby the sync code can be reducedto ¼ pattern, which increases the efficiency.

The following explains the scalability of this data structure withreference to FIG. 22. As is shown in FIG. 22(c), in the presentinvention, the recording capacity can be between, for example, 12 byteand 188 byte, and can be arbitrarily raised by steps of 16 byte. FIG.21(a) shows that n can change between n=1 to n=12. If, for example, n=1,as in FIG. 21(b), there are only four-data rows 951 a, 951 b, 951 c, and951 d, and the following rows are the ECC rows 952 a, 952 b, 952 c, and952 d. The data row 951 d becomes the 4-byte EDC row. Thus, theremaining rows 951 e to 951 z are taken to be filled with 0's, and errorcorrection-coding is performed. This ECC encoding is performed by theECC encoder 907 if the laser recording apparatus in FIG. 15, andrecorded as a barcode on the disk. If n=1, only 12 bytes can be recordedover an angular range of 510. Similarly, if n=2, 18 bytes are recorded,and if n=12, 271 bytes are recorded over an angular range of 336°.

In the present invention, this scalability has a purpose. Moreover, theproduction tact time is important for the laser trimming. If the BCArecording areas are trimmed one by one, a slow apparatus can take morethan 10 seconds to record a maximum of several thousands. Since theproduction tact time is four seconds, this will slow down the productiontact time. On the other hand, the main object for application of thepresent invention is first of all the disk ID, for which about 10 bytesshould suffice. If 271 bytes are written instead of 10 bytes, the laserprocessing time will rise six-fold, so that the production costincreases. Employing the scalability method of the present invention canreduce production cost and time.

The ECC encoder 930 b of the recording/reproduction apparatus in FIG.14, can error-correct data from 12 bytes to 271 bytes with the sameprogram, by, for example, filling up the rows 951 e to 951 z with 0's ifn=1 as in FIG. 21(b).

As is shown in FIG. 24, for 1T, the pulse width of 4.4 μs becomes aboutone half of the stripe interval of 8.92 μs. For 2T, the pulse width is4.4 μs for a stripe interval of 17.84 μs, and for 3T, the pulse width is4.4 μs for a stripe interval of 26.76 μs, so that, taking the averagefor a PE-RZ modulation, about ⅓ corresponds to the pulse portion(reflection coefficient about zero). Consequently, in a disk with astandard reflection coefficient of 70%, the reflection coefficient dropsto about ⅔, that is, to about 50%, and thus can be reproduced with aregular ROM disk player.

Moreover, in magneto-optical disks, the average refractive index of therecording layer does not change, and the average change of thereflection coefficient is less than 10%, so that level fluctuations ofthe reproduction waveform are small and compatibility with DVD playersis easy.

The following is an explanation of the reproduction order with referenceto the flowchart in FIG. 25. When the disk is inserted, first, the TOC(Control Data) is reproduced (step 940 a). In optical disks according tothe present invention, a stripe existence identifier 937 is recorded asa pit signal in the TOC of the TOC region 936, as is shown in FIG. 19.Therefore, when the TOC is reproduced, it can be verified whetherstripes are recorded or not. Then, it is determined whether the stripeexistence identifier 937 is “0” or “1” (step 940 b). If the stripeexistence identifier 937 is “0”, the optical head moves towards theouter perimeter of the optical disk, switches to rotation phase controland performs a regular CLV reproduction (step 940 f). If the stripeexistence identifier 937 is “1”, it is determined whether the stripesare on the opposite side of the reproduction side, that is, whether theyare recorded on the reverse side of the disk (the reverse-side stripeexistence identifier 948 is “1” or “0”) (step 940 h). If thereverse-side stripe existence identifier 948 is “1”, the recording layeron the reverse side of the optical disk is reproduced (940 i). If thereverse side of the optical disk cannot be reproduced automatically, areverse-side reproduction instruction is given out and displayed. If itis known in step 940 h that stripes are recorded on the side that isbeing reproduced, the optical head is moved to the region of the stripes923 on the inner perimeter of the optical disk (step 940 c), therotation speed control is switched, and the stripes 923 are reproducedwith CAV rotation (step 940 d). Then, it is determined whether thereproduction of the stripes 923 has finished (step 940 e). If thereproduction of the stripes 923 has finished, the optical head movestowards the outer perimeter of the optical disk, switches again torotation phase control, and performs regular CLV regeneration (step 940f), to regenerate the data of the pit signals (step 940 g).

Thus, by recording a stripe existence identifier 937 in the pit regionof the TOC, the stripes 923 can be reliably reproduced. If the stripeexistence identifier on the optical disk is not defined, the region ofthe stripes 923 cannot be properly tracked, so that time has to be spentto discriminate between stripes 923 and defects. In other words, evenwhen there are no stripes, an attempt is made to read the stripes, andit has to be verified in a separate step, whether there are really nostripes, or whether they are perhaps located even more towards the innerperimeter, so that extra time is needed to start up the reproductionprocess. Moreover, since the reverse-side stripe existence identifier948 has been recorded, it can be determined whether the stripes 923 arerecorded on the reverse side. Therefore, even in the case of an opticaldisk such as a double-sided DVD, the barcode stripes 923 can be reliablyreproduced. In a DVD-ROM, the inventive stripes pass through bothreflecting layers of a double-sided disk, so that they also can be readfrom the reverse side. Reading the reverse-side stripe existenceidentifier 948, the stripes 923 can be reproduced from the reverse sideby encoding the stripes backwards at recording time. As is shown in FIG.22(a) the present invention uses “01000110” for the synchronized coding.Consequently, when reproduced from the reverse side, the synchronizedcoding “01100010” is detected. Therefore, it can be detected whether thebarcode stripes 923 are reproduced from the reverse side. In that case,a second decoder 930 of the recording/reproduction apparatus of FIG. 14decodes the code backwards, so that even when a double-sided disk isreproduced from the reverse side, the penetrating barcode stripes 923can be correctly reproduced. Moreover, as is shown in FIG. 19, awrite-once stripe data existence identifier 939 and the stripe recordingcapacity are recorded in the TOC. Consequently, when stripes 923 havealready been recorded in a first trimming, the recordable amount for asecond trimming of stripes 938 can be calculated. Therefore, when therecording apparatus in FIG. 15 performs the second trimming, it can bedetermined from the TOC data how much more can be recorded. As a result,it can be prevented that the recording exceeds 360° and the stripes 923of the first trimming are destroyed. As is shown in FIG. 19, by leavingan empty portion 949 of at least one pit signal frame between thestripes 923 of the first trimming and the stripes 938 of the secondtrimming, it can be prevented that the previous trimming data isdestroyed.

Since a trimming counter identifier 947 is recorded in the synchronizedcoding portion, as shown in FIG. 22(b), the stripes 923 of the firsttrimming and the stripes 938 of the second trimming can bediscriminated. If there were no trimming counter identifier 947, thefirst stripes 923 and the second stripes 938 could not bedifferentiated.

The following is an explanation of the procedure from contents to diskproduction with reference to FIG. 33. As is shown in FIG. 33, first, theoriginal contents 3 of, for example, a motion picture are encoded inblocks with a variable length scheme and turned into a compressed videosignal, such as image-compressed MPEG, in a disk manufacturing portion19. This signal is scrambled by the encryption encoder 14 with theencryption key 20 for activation. This scrambled compressed video signalis recorded as a pit-shaped signal on a master disk 6 with the masterdisk production apparatus 5. Using the master disk 6 (or a molding die,or a stamper) and a molding apparatus 7, a large-volume disk substrate 8with recorded pits is manufactured and a reflecting layer of, forexample, aluminum is formed with a reflecting layer forming apparatus15. Two disk substrates 8 and 8 a are laminated with a laminatingapparatus 9 to finish a laminated disk 10. In case of a magneto-opticaldisk, the compressed video signal is recorded as a magneto-opticalsignal in the recording layer. In case of a single-sided disk, the disk240 a is finished without laminating. In case of a DVD-RAM disk, thecompressed video signal is similarly recorded in the recording layer,and two disk substrates are laminated with a laminating apparatus 9 tofinish laminated disk 300. For DVD-RAMs, there are single-sided diskswith a recording layer only on one side, and double-sided with arecording layer on both sides.

As shown in FIG. 38(a), in a BCA recording with a laser, a pulsed laser808 irradiates laser light on an aluminum reflection film 809 of alaminated disk 800, so that stripe-shaped low-reflection portions 810are recorded as PC modulation signals by trimming the aluminumreflection film 809. Thus, as shown in FIG. 38(b), BCA stripes areformed on the disk. When these BCA stripes are reproduced with a regularoptical head, the reflection signal from the BCA portion disappears, sothat the modulation signal is generated from the signal-lacking portions810 a, 810 b, 810 c, which are intermittently lacking a modulationsignal. A modulation signal with 8-16 modulation of the pits is slicedat a first slice level 915 to decode the main signal. On the other hand,since the signal level of the signal-lacking portion 810 a is low, iteasily can be sliced at the second slice level 916. The barcodes 923 aand 923 b shown in FIG. 39(b) are sliced at the slice level S2 shown inFIG. 39(e), so that they can be reproduced with a regular opticalpickup. As is shown in FIG. 39(f), a digital signal can be attained byslicing the signal, after suppressing high-frequent pit signalcomponents with a low-pass filter, at the second slice level S2. ByPE-RZ-decoding this digital signal, a digital signal as shown in FIG.39(g) is output. The actual appearance of the reproduction signal isshown in FIG. 31.

The following is an explanation of the decoding with reference to FIG.14.

As is shown in FIG. 14, a disk 800 with a BCA includes two transparentsubstrates that are laminated together with the recording layer 802 a onthe inside. There may be one recording layer 802 a or two recordinglayers 802 a and 802 b. When there are two recording layers, a stripeexistence identifier 937 (see FIG. 19) indicating whether there is a BCAis recorded in the control data of the first recording layer 802 a nearthe optical head 255. In this case, because the BCA is in the secondrecording layer 802, the focus is on the first recording layer 802 a,and the optical head 255 is moved to the radial position of the controldata on the innermost perimeter of the second recording region 919.Since the control data is main information, it is recorded by EFM, 8-15,or 8-16 modulation. Only when the stripe existence identifier 937 in thecontrol data is “1”, the one-layer/two-layer switching portion 827changes the focus to the second recording layer 802 b to reproduce theBCA. Using the first level slice portion 590 and slicing at a regularfirst slice level 915 as shown in FIG. 38(c), the BCA is converted intoa digital signal. This signal is decoded by an EFM decoder 925, an 8-15modulator-decoder 926 or an 8-16 modulator-decoder 927 in the firstdecoder 928. Then it is error-corrected by the ECC decoder 36, andoutput as main information. The BCA is only read out when the controldata in this main information is reproduced and the stripe existenceidentifier is “1”. When the stripe existence identifier 937 is “1”, theCPU 923 issues an instruction to the one-layer/two-layer switchingportion 827, and drives the focus adjusting portion 828 to switch thefocus from the first recording layer 802 a to the second recording layer802 b. At the same time, the optical head 255 is moved to the radialposition of the second recording region 920 (in the DVD standard, thisis the BCA recorded between 22.3 mm and 23.5 mm from the inner perimeterof the control data), and the BCA is read out. In the BCA region, theenvelope of the partially missing signal in FIG. 38(c) is reproduced. Bysetting the luminous energy for the second slice level 916 of the secondlevel-slice portion 929 below the first slice level 915, the reflectionportions and the missing portions of the BCA can be detected, and thedigital signal output. This signal is decoded in the PE-RZ decoder 930 aof the second decoder 930 and ECC-decoded in the ECC decoder 930 b togive out the BCA data, which is auxiliary information. Thus, the maininformation is decoded and reproduced by the first decoder 928, and theBCA data, which is auxiliary information, is decoded and reproduced bythe second decoder.

FIG. 24(a) shows the reproduction waveform before passing the low-passfilter 943, FIG. 24(b) shows the processing precision of the slits inthe low-reflection portion, and FIG. 23(b) shows the simulated waveformafter passing the low-pass filter 943. It is difficult to provide slitswith a width below 5-15 μm. Moreover, if a recording is performedfurther than 23.5 mm from the disk center, the recording data will bedestroyed. For DVDs, the largest capacity after formatting is limited to188 bytes, due to the limitations of the shortest recording period of 30μm, and the largest radius of 23.5. mm.

The following is a detailed specific example for setting the secondslice level 916 and the operation of the second level slice portion 929.

FIG. 26 is a detailed view of the second level slice portion 929. Thewaveform for this explanation is shown in FIG. 27.

As is shown in FIG. 26, the second level slice portion 929 comprises alight-reference-value setting portion 588 feeding the second slice level916 to the second level slicer 587, and a frequency divider 587 d forfrequency-dividing the output signal of the second level slicer 587.Moreover, the light-reference-value setting portion 588 comprises alow-pass filter 588 a and a level converter 588 b.

The following explains its operation. In the BCA region, the envelope ofthe partially missing signal as shown in FIG. 27(a) is reproduced due tothe BCA. In this reproduction signal, high-frequency components due tothe signal and low-frequency components due to the BCA signal are mixed.However, the high-frequency components of the 8-16 modulation can besuppressed with the low-pass filter 943, and only the low-frequencysignal 932 of the BCA signal as shown in FIG. 27(b) is entered into thesecond level slicer 929.

When the low-frequency signal 932 is entered into the second level sliceportion 929, the light-reference-value setting portion 588 filters outeven lower frequency components (almost DC) of the low-frequency signal932 with a low-pass filter 588 a with a time constant that is largerthan the time constant of the low-pass filter 943 (in other words, thelow-pass filter 588 a extracts low-frequency components). The levelconverter 588 b adjusts the signal to a suitable level, so that a secondslice level 916 as illustrated by the fat line in FIG. 27(b) is output.As is shown in FIG. 27(b), the second slice level 916 tracks theenvelope.

In the present invention, when the BCA is read, a rotation phase controlcannot be performed, and tracking control is also not possible.Consequently, the envelope incessantly fluctuates as in FIG. 27(a). Ifthe slice level were constant, the fluctuating reproduction signal couldbe mistaken, causing the error rate to go up. Therefore, it would not beappropriate to carry data. However, with the circuit in FIG. 26 of thepresent invention, the second slice level is constantly corrected andfitted to the envelope, so that wrong slicing can be significantlyreduced.

Thus, the present invention is not affected by a fluctuating envelope,and the second level slicer 587 slices the low-frequency signal 932 atthe second slice level 916, before outputting a binarized digital signalsuch as the one shown in FIG. 27(c). At the start of the binarizeddigital signal output from the second level slicer 587, the signal isreversed, and a digital signal as shown in FIG. 27(d) is output.Accordingly, FIG. 28 shows the specific circuits for a frequencydividing means 934 and a second level slice portion 929.

Thus, by setting the second slice level 916, differences in thereflection coefficient of different disks, variations in the luminousenergy due to aging of the reproduction laser, and low-frequency level(DC level) variations of the 8-16 modulation signal due totrack-crossing at reproduction time can be absorbed, and a reproductionapparatus for optical disks can be provided that can reliably slice theBCA signal.

The following explains another method for slicing the second slice level916. FIG. 29 shows another circuit diagram for the frequency dividingmeans 934 and the second level slice portion 929. As is shown in FIG.29, the low-pass filter 943 of the frequency dividing means 934comprises a first low-pass filter 943 a with a small time constant and asecond low-pass filter 943 b with a large time constant. The secondlevel slicer 587 of the second level slice portion 929 comprises aninverting amplifier 687 a, a DC reproduction circuit 587 b, a converter587 c, and a frequency half-divider 587 d. The waveform for this exampleis shown in FIG. 31.

The following explains its operation. In the BCA region, the envelope ofthe partially missing signal as shown in FIG. 31(a) is reproduced due tothe BCA. This reproduction signal is entered into a first low-passfilter 943 a and a second low-pass filter 943 b of the low-pass filter943. The first low-pass filter 943 a with the smaller time constanteliminates the high-frequency signal components of the 8-16 modulationfrom the reproduction signal, and outputs the BCA signal. The firstlow-pass filter 943 b with the larger time constant passes the DCcomponents of the reproduction signal, and outputs the DC component ofthe reproduction signal. When the first low-pass filter 943 a suppressesthe high-frequency components of the 8-16 modulation and enters thissignal into the inverting amplifier 587 a, the inverting amplifier 587 aamplifies the amplitude, which has been reduced by passing through thefirst low-pass filter 943 a. The amplified signal is DC-reproduced atGND level in the DC reproduction circuit 587 b, and a signal as shown inFIG. 31(c) is entered into the comparator 587 c. On the other hand, whenthe second low-pass filter 943 b enters the DC component of thereproduction signal into the light-reference-value setting portion 588,the light-reference-value setting portion 588 adjusts the signal with aresistive divider to an appropriate level and enters the second slicelevel 916 into the comparator 587 c, as shown in FIG. 31(b). Thecomparator 587 c slices the output signal of the CD reproduction circuit587 b at the second slice level 916 and outputs a binarized digitalsignal as shown in FIG. 31 (d). At the start of the digital signal,which has been binarized by the comparator 587 c, the frequencyhalf-divider 587 d reverses the signal, and a digital signal is output.Accordingly, FIG. 28 shows the specific circuits for a frequencydividing means 934 and a second level slice portion 929.

FIG. 30 shows a specific circuit of the frequency dividing means 934 andthe second level slice portion 929 to accomplish this.

Thus, by setting the second slice level 916 to reproduce the BCA signal,differences in the reflection coefficient of different disks, variationsin the luminous energy due to aging of the reproduction laser, andlowfrequency level (DC level) variations of the 8-16 modulation signaldue to track-crossing at reproduction time can be absorbed, andreproduction apparatus for optical disks can be provided that can slicethe BCA signal reliably. Moreover, when the circuits are discrete, thenumber of elements can be minimized, and a reliable BCA reproductioncircuit can be achieved.

Moreover, if this signal can be loaded into the CPU and decoded bysoftware, the clock frequency of the PE modulation signal can be reducedto one half with the frequency half-divider 587 d. Therefore, even whena CPU with a slow sample frequency is used, the threshold of the signalcan be detected reliably.

This effect also can be attained by slowing down the rotation frequencyof the motor at reproduction time. This will be explained with FIG. 14.When the command has been issued to reproduce the BCA, the CPU sends arotation speed deceleration signal 923 b to the rotation controller 26.Then, the rotation controller 26 decelerates the rotation frequency ofthe motor 17 to one half or one quarter. Therefore, the frequency of thereproduction signal decreases, and can be decoded by software even whena CPU with a slower sample frequency is used, and a BCA with a smalllinewidth can be reproduced. Sometimes, production facilitiesmanufacture BCA stripes with a small linewidth, but by slowing down therotation frequency they can be handled with slow CPUs. This improves theerror rate and the reliability at BCA reproduction time.

When the BCA is read at a regular speed (such as single speed), the CPU923 sends a deceleration command to the rotation controller 26 to halvethe rotation frequency of the motor 17 only when an error occurred inthe BCA reproduction. Adopting this method, the actual read-out speedfor a BCA with an average linewidth does not decrease at all. Only whenthe linewidth is narrow and errors occur, the errors can be correctlydetected by reading the BCA at half the speed. Thus, by slowing down theread-out speed for narrow BCA linewidths, a slowdown of the BCAreproduction speed can be prevented.

In FIG. 14, a low-pass filter 943 is used as the frequency dividingmeans 934 but an envelope-tracking circuit or a peak-hold also can beused as long as it is a means for suppressing high-frequency signals ofthe 8-16 modulation from the reproduction signal of the BCA region.

The frequency dividing means 934 and the second level slicer 929 alsocan be means for directly binarizing the reproduction signal of the BCAregion, then entering the reproduction signal into a microprocessor,discriminating the 8-16 signal and the BCA signal on the time axis bydigitally processing using points with difference of edge intervals, andsubstantially suppressing the high-frequency signal of the 8-16modulation.

The modulation signal is recorded with pits by 8-16 modulation to obtainthe high-frequency signal 933 in FIG. 14. On the other hand, the BCAsignal becomes the low-frequency signal 932. Thus, since in the DVDstandard, the main information is a high-frequency signal 933 of amaximum of 4.5 MHz, and the auxiliary information is a low-frequencysignal 932 with a period of 8.92 μs, that is, about 100 kHz, theauxiliary information easily can be frequency-divided with the low-passfilter 943. Using a frequency dividing means 934 comprising a low-passfilter 943 as shown in FIG. 14, the two signals easily can be divided.In this case, the low-pass filter 943 can be of a simple configuration.

The preceding was an outline of the BCA.

FIG. 32 is a block drawing of a disk manufacturing apparatus and areproduction apparatus. As is shown in FIG. 32, the disk manufacturingportion 19 manufactures laminated ROM or RAM disks or single-substratedisks 10 with the same contents. Using a BCA recorder 13, the diskmanufacturing apparatus 21 PE-modulates BCA data 16 a, 16 b, 16 cincluding the identification codes 12 a, 12 b, 12 c, such as IDs thatare different for each disk, and forms barcode-shaped BCAs 18 a, 18 b,18 c on the disks 10 a, 10 b, 10 c by trimming with a YAG-laser. In thefollowing, the disks whereon a BCA 18 has been recorded are referred toas BCA disk 11 a, 11 b, and 11 c. As is shown in FIG. 32, the pitportion and the recording signal on the BCA disks 11 a, 11 b, and 11 care completely the same. However, a different (for example,incrementally numbered) ID is recorded into the BCA 18 of each disk.Contents providers, such as film studios, can record these IDs into anID data base 22. When the disks are shipped, the BCA data is read with abarcode reader 24 that can read BCA, and it is recorded which disk withwhich ID has been distributed at what time to which system operator 23,that is, CATV studio, broadcasting station or airline.

A record about which disk ID has been distributed to which systemoperator at what time is recorded in the ID data base 22. Therefore, ifa large number of illegal copies of a certain BCA disk is put intocirculation, it can be traced by checking the real watermark to whichsystem operator the illegally copied disk had been originallydistributed. This feature will be detailed further below. Since this IDnumbering based on the BCA performs virtually the same role as awatermark for the entire system, it is called “prewatermarking”.

The following is an explanation of the data to be recorded in the BCA.An ID generator 26 generates IDs. Moreover, a watermark-productionparameter generator 27 generates watermark-production parameters basedon these IDs or on random numbers. Then, the ID and thewatermark-production parameters are mixed signed by a digital signatureportion 28 using the private key of a public key cryptography. The BCArecorder 13 records the ID, the watermark-production parameters and thesignature data onto each disk 10 a, 10 b, and 10 c. Thus, the BCAs 18 a,18 b, and 18 c are formed.

If main information, such as a video signal, is recorded on the BCAdisks 11 a, 11 b, or 11 c, the BCA reproduction portion 39 first readsout the BCA signal including the different IDs, as shown in FIG. 41.Then, a watermark recording portion 264 converts the video signal bysuperimposing the BCA signal and a recording circuit 272 records theconverted video signal on the BCA disks 11 a, 11 b, and 11 c (300 (240,800) in FIG. 41). When the video signal onto which the BCA signal hasbeen superimposed is reproduced from the BCA disk 300 (240, 800), theBCA reproduction portion 39 reads out the BCA signal of the disk, anddetects it as the ID1 of the disk. A watermark reproduction portiondetects the video signal onto which the watermark has been superimposedas disk ID2. A comparator compares the ID1 read out from the BCA signalwith the disk ID2 read out from the watermark of the video signal, andwhen the two IDs do not match, the reproduction of the video signal isstopped. As a result, the video signal of an illegal disk onto which awatermark that is different from the BCA signal has been superimposedcannot be replayed. On the other hand, if both IDs match, a descrambler31 descrambles the video signal with the superimposed watermark using acompound key comprising ID information read out from the BCA signal, andthe video signal is output.

The BCA disks 10 a, 10 b, and 10 c that have been “pre-watermarked” withsuch a disk manufacturing apparatus 21 are then sent to the systemoperators 23 a, 23 b, and 22 c with the reproduction apparatuses 25 a,25 b, and 25 c. In FIG. 32, elements of the broadcasting apparatus 28have been partially left out for the sake of convenience.

FIGS. 34 and 35 illustrate the operation performed by the systemoperators. FIG. 34 is a block diagram showing the broadcasting apparatus28 in detail. FIG. 35 is a graph showing the waveform of the originalsignal and the video signals on the time axis and their waveforms on thefrequency axis.

As is shown in FIG. 34, the broadcasting apparatus 28 set up in a CATVstation comprises a reproduction apparatus 25 a for system operators,and the disk 11 a with BCA supplied by, for example, the film studio, isinserted into this reproduction apparatus 25 a. The main information ofthe signal that is reproduced with the optical head 29 is reproducedwith the data reproduction portion 30, descrambled with the descrambler31, expanded to the original movie signal with the MPEG decoder 33, andsent to the watermark portion 34. The original signal as shown in FIG.35(a) is first entered into the watermark portion 34, and transformedby, for example, FFT from the time domain into the frequency domain by afrequency converter 34 a. Thus, the frequency spectrum 35 a shown inFIG. 35(b) is attained. A spectrum mixer 36 mixes the frequency spectrum35 a with the ID signal having the spectrum shown in FIG. 35(c). Asshown in FIG. 35(d), the spectrum 35 b of the mixed signal is the sameas the frequency spectrum 35 a of the original signal shown in FIG.35(b). In other words, the ID signal is spectrally dispersed. Thissignal is transformed from the frequency domain to the time domain by,for example, inverse FFT with an inverse frequency converter 37, and asignal as in FIG. 35(e), which is almost the same as the original signal(FIG. 35(a)) is obtained. Because the ID signal is spectrally dispersedin the frequency domain, the deterioration of the video signal isnegligible.

A digital signature verification portion 40 verifies the signature ofthe BCA data reproduced from the BCA disk 11 a by the BCA reproductionportion 39 with, for example, the public key sent from, for example, anIC card 41. If the signature is invalid, the operation is halted. If thesignature is valid, this shows that the data has not been manipulatedand the ID is sent unchanged to a watermark-data production portion 41a. Using the watermark-production parameters contained in the BCA data,a watermark signal corresponding to the ID signal shown in FIG. 35(c)can be generated. The watermark signal also can be generated bycalculating the watermark from the ID data or the card ID of the IC card41.

In that case, the ID has absolutely nothing to do with thewatermark-production parameters, so that if the watermark-productionparameters and the ID are recorded in the BCA, the watermark can not bededucted from the ID. In other words, only the copyright owner knows therelation between ID and watermark. Therefore, watermarks being illegallyissued to make illegal copies and issue new IDs can be prevented.

On the other hand, a spectral signal can be generated by a certaincalculation from the card ID of the IC card 41 to bury the card ID ofthe IC card 41 as a watermark in the video output signal by adding it tothe ID signal 38. In this case, both the circulated (that is, suppliedby sales) ID of the software and the ID of the reproduction apparatuscan be verified so that the tracing of illegal copies becomes easy.

The video output signal of the watermark portion 34 is sent to theoutput portion 42. If the broadcasting apparatus 28 broadcasts acompressed video signal, the video output signal is compressed with anMPEG encoder 43, scrambled with a scrambler 45 using the systemoperator's own encryption key 44 and broadcast from the broadcastingportion 46 to the audience via a network or radio waves. In this case,the compression parameter information, such as the transfer rate afterthe original MPEG signal has been compressed, is sent from the MPEGdecoder 33 to the MPEG encoder 43, so that the compression ratio can beincreased even with real-time encoding. Moreover, the compressed audiosignal 48 can bypass the watermark portion 34 to avoid expansion andcompression, so that a deterioration of the audio quality can beavoided.

Then, if no compressed signal is broadcast, the video output signal 49is scrambled unchanged and broadcast from the broadcasting portion 46 ato the audience via a network or radio waves. In video systems on boardairplanes, scrambling is unnecessary. Thus, a video signal with awatermark is broadcast from the disk 11 a with BCA.

An illegally copied recording medium 56, for example a video tape or aDVD laser disk is reproduced with a reproduction apparatus 55 a, such asa VTR or a DVD player. The reproduced video signal 49 b is fed into afirst input portion of a watermark detection apparatus 57. A firstspectrum 60, which is a spectrum of the illegally copied signal, asshown in FIG. 35(g) is obtained with a first frequency converter 59 aby, for example, FFG or DCT. The original contents are fed into a secondinput portion 58 a, and a second spectrum 35 a is obtained bytransformation into the frequency domain with a second frequencyconverter 59 a. Such a spectrum is shown in FIG. 35(b). When thedifference between the first spectrum 60 and the second spectrum 35 a istaken with a subtractor 62, a differential spectrum signal 63 as shownin FIG. 35(h) can be obtained. This differential spectrum signal 63 isgiven into an ID detector 64. The ID detector 64 retrieves the watermarkparameters for the n-th ID from an ID database 22 (step 65), inputs them(step 65 a), and compares the spectrum signal based on the watermarkparameters with the differential spectrum signal 63 (step 65 b). Then,it is determined whether the spectrum signal based on the watermarkparameters and the differential spectrum signal 63 match. If the twomatch, this means the ID corresponds to the n-th watermark, so that ID=n(step 65 d). If the two do not match, ID is renewed to n+1, and thewatermark for the (n+1)th watermark is retrieved from the ID database.These steps are repeated to detect the ID of the watermark. If the IDmatches, the spectrums in FIGS. 35(c) and 35(h) [(3) and (8)] match. TheID of the watermark is output from an output portion 66, and it can beseen from where the unauthorized copy came.

Thus, the receiver 50 on the user side receives the watermarked videosignal 49 transmitted with a transmitter 46 of the broadcastingapparatus 28 on the system-operator side, as is shown in FIG. 36. In thereceiver, a second descrambler 51 cancels the scrambling, and if thesignal is compressed, an MPEG decoder 52 expands the signal, which isthen output from an output portion 53 as a video signal 49 a to amonitor 54.

The following discusses the illegal copying. The video signal 49 a canbe intercepted and recorded on a tape 56 with a VTR 55, and a largenumber of illegal copies of the tape 56 thus can be multiplied andcirculated (by sales), resulting in an infringement of the rights of thecopyright holder. However, if the BCA of the present invention is used,there is a watermark in the video signal 49 a and in the video signal 49b (see FIG. 37) that is reproduced from a video tape 56. Because thewatermark has been added in the frequency domain, it cannot be easilyeliminated. Also, it cannot be eliminated by passing the signal througha regular recording/reproduction system.

The following is an explanation of how the watermark can be detected,with reference to FIG. 37.

An illegally copied recording medium 56, for example a video tape or aDVD laser disk is reproduced with a reproduction apparatus 55 a, such asa VTR or a DVD player. The reproduced video signal 49 b is fed into afirst input portion of a watermark detection apparatus 57. A firstspectrum 60, which is a spectrum of the illegally copied signal, asshown in FIG. 35 (7) is obtained with a first frequency converter 59 aby, for example, FFG or DCT. The original contents are fed into a secondinput portion 58 a, and a second spectrum 35 a is obtained bytransformation into the frequency domain with a second frequencyconverter 59 a. Such a spectrum is shown in FIG. 35 (2). When thedifference between the first spectrum 60 and the second spectrum 35 a istaken with a subtractor 62, a differential spectrum signal 63 as shownin FIG. 35 (8) can be obtained. This differential spectrum signal 63 isgiven into an ID detector 64. The ID detector 64 retrieves the watermarkparameters for the n-th ID from an ID database 22 (step 65), inputs them(step 65 a), and compares the spectrum signal based on the watermarkparameters with the differential spectrum signal 63 (step 65 b). Then,it is determined whether the spectrum signal based on the watermarkparameters and the differential spectrum signal 63 match. If the twomatch, this means the ID corresponds to the n-th watermark, so that ID=n(step 65 d). If the two do not match, ID is renewed to n+1, and thewatermark for the (n+1)th watermark is retrieved from the ID database.These steps are repeated to detect the ID of the watermark. If the IDmatches, the spectrums in FIGS. 35, (3) and (8) match. The ID of thewatermark is output from an output portion 66, and it can be seen fromwhere the unauthorized copy came.

Thus, because the ID of the watermark can be determined as describedabove, the origin of the pirated disks or unauthorized copies can betraced, so that the copyright can be protected.

If a system that combines the BCA of the present invention with awatermark records the same video signal on a ROM disk or a RAM disk, andrecords watermark information in the BCA, it can realize a virtualwatermark. The system operator can bury watermarks corresponding to theIDs that are issued to the contents providers in the video signal thatis eventually output from the reproduction apparatus. Compared withconventional methods for recording video signals with watermarks thatdiffer for each disk, the disks' cost and production time can be reducedsignificantly. A watermark circuit is needed in the reproductionapparatus, but since FFT and IFFT are staple techniques, this will notplace an undue burden upon the broadcasting devices.

In this example, a spectrum-dispersion watermark portion was used, butthe same effect can be obtained with other types of watermark portionsas well.

For a DVD-RAM disk 300 or a magneto-optical disk 240, a contentsprovider having, for example, a CATV station with the DVDrecording/reproduction apparatus shown in FIG. 14 or the magneto-opticalrecording/reproduction apparatus shown in FIG. 42 sends the scrambleddata, which has been encrypted with the ID number in the BCA as one key,to another recording/reproduction apparatus on the user side via acommunication line, and the scrambled data is temporarily recorded onthe DVD-RAM disk 300 a or magneto-optical disk 240 a of, for example,the CATV station. To reproduce the scrambled signal from the samemagneto-optical disk 240 a is authorized use, so that the BCA is read,and the signal is descrambled in a descrambling portion, that is, theencryption decoder 534 a, using the BCA data obtained from the BCAoutput portion 750 as the decryption key, as shown in FIG. 42. Then, theMPEG decoder 261 expands the MPEG signal to obtain the video signal. If,however, the scrambled data, that is recorded on the magneto-opticaldisk 240 a for authorized use, is copied onto a magneto-optical disk 240b, that is, unauthorized use is made, the correct decryption key fordescrambling the scrambled data cannot be obtained during reproduction,because the BCA data of the disks are different, so that the encryptiondecoder 534 a cannot descramble the signal. Therefore, the video. signalcannot be output. Therefore, a signal that is illegally copied ontoanother magneto-optical disk 240 b cannot be reproduced, so that thecopyright can be protected. In effect, the contents can be recorded onand reproduced from only one magneto-optical disk 240 a. The same istrue for the DVD-RAM disk 300 a shown in FIG. 14, where the contentsalso can be recorded on and reproduced from only one disk.

The following is an explanation of an even tougher protection method.First, the BCA data of the magneto-optical disk 240 on the user side aresent via communication line to the contents provider. Then, on thecontents provider side, the video signal is transmitted with the BCAdata buried inside the video signal as a watermark by the watermarkrecording portion 264. On the user side, this signal is recorded onto amagneto-optical disk 240 a. During reproduction, a watermarkreproduction verification portion 262 verifies the BCA data of therecording permission identifier and the watermark against the BCA dataobtained by the BCA output portion 750, and authorizes compoundreproduction only if they match. This makes the protection of copyrightseven stronger. Since with this method the watermark can be detected bythe watermark reproduction portion 263 even if a digital/analog copy istaken directly to video tape from the magneto-optical disk 240 a, theproduction of illegal digital copies can be prevented or detected. As inthe case of the DVD-RAM disk shown in FIG. 14, the production of illegaldigital copies can be prevented or detected.

In this case, by providing the magneto-optical recording/reproductionapparatus or the DVD recording/reproduction apparatus with a watermarkreproduction portion 263, a recording prevention portion 265 authorizesthe recording only if there is a watermark indicating a “first recordingpossible identifier” in the signal received from the contents provider.The recording prevention portion 265 and a “first recording completionidentifier”, which is discussed below, prevent a second recording of thedisk, that is, illegal copying. Moreover, an identifier showing “firstrecording completed” and an individual disk number of themagneto-optical disk 240 a pre-recorded in the BCA recording portion 220are overlapped by the watermark recording portion 264 with the recordingsignal with the primary watermark and buried and recorded on themagneto-optical disk 240 a as the second watermark. If the data fromthis magneto-optical 240 a are descrambled or converted to analog andrecorded onto other media, for example, a video tape or a DVD-RAM, thenthe “first recording completion identifier” can be detected if the VTRor the like comprises a watermark reproduction portion 263. Thus, therecording prevention portion 265 impedes the recording of a second tapeor disk, so that illegal copies are prevented. If the VTR is notequipped with a watermark production portion 263, an illegal copy can beproduced. However, by examining the watermark of the illegally copiedvideo tape, the recording history, for example, the name of the contentsprovider can be reproduced from the recording data of the primarywatermark, and the BCA disk ID of the first, legal recording can bereproduced from the buried secondary watermark, so that a follow-upcheck can be made from which contents provider which (or whose) disk hasbeen provided on which date. Consequently, the individual who broke thelaw can be identified and tried for copyright infringement, so thatillegal copies and plans for similar actions by the same infringer canbe indirectly impeded. Since the watermark does not disappear even whenconverting the signal to analog, this is also useful for analog VTRs.

The following is an explanation of a recording apparatus that can recordor transmit illegally by circumventing the copy protection even though awatermark indicating “first recording complete” or “recording forbidden”is detected and by adding a circuit producing a scrambling key. Thiscase cannot be prevented directly, but the circumvention circuit becomesextremely complicated. Moreover, as has been explained above, therecording history can be ascertained from the primary and the secondarywatermark, so that illegal copies and illegal use can be preventedindirectly, similar to the case explained above.

The following is an explanation of the particular effects of the BCA.The BCA data specify the disk, and with the BCA data the primary user ofthe contents, who is recorded in data base of the contents provider, canbe specified. Therefore, by adding the BCA, the tracing of illegal usersbecomes easy when watermarks are used.

Moreover, as is shown by the recording circuit 266 in FIGS. 14 and 42,BCA data are used for a portion of the encryption key for scrambling,and for the primary watermark or the secondary watermark, so that whenboth are checked for by the watermark reproduction portion 263 of thereproduction apparatus, an even stronger copy protection can berealized.

Moreover, a watermark or scrambling key, to which a time informationinput portion 269 has added the authorization dates from systemoperators such as rental stores, is input into a scrambling portion 271,and synthesized into a password 271 a. When the reproduction deviceperforms a verification of the date information using the password 271 aor the BCA data or the watermark, a period wherein the scrambling keycan be cancelled can be specified, for example as “3 days use possible”,in the encryption decoder 534 a. This also can be used for a rental disksystem, which can be protected with the copy prevention technology ofthe present invention, resulting in strong copyright protection andmaking illegal use very difficult.

As explained above, when the BCA is used for a rewritable optical disk,such as a magneto-optical disk used for an ASMO, the copyrightprotection through watermarks or scrambling can be strengthened evenfurther.

Moreover, the above embodiments have been explained for a DVD ROM diskof two laminated disks, a RAM disk and a single-substrate optical disk.However, the present invention can be applied regardless of the diskstructure to any kind of disk with the same effect. In other words,recording the BCA on other types of ROM disks or RAM disks, on DVD-Rdisks, or magnet o ptical disks, the same recording properties andreliability can be attained. The above explanations are equallyapplicable to DVD-R disks, DVD-RAM disks and magneto-optical disks, withthe same results, but these explanations have been omitted.

Moreover, the BCA identifying information in the above embodiments havethe same information signal format for DVDs and for magneto-opticaldisks, so that using an optical head for magneto-optical disks with thestructure in FIG. 7, the BCA identifying information for DVDs can bereproduced. And, in this case, an excellent reproduction signal of theBCA identifying information with a small error rate can be attained witha reproduction filter and by adjusting the decoding conditions duringreproduction.

Moreover, since in the magneto-optical disk of the above embodiments,only the magnetic properties of the recording layer are changed,excellent reliability can be achieved in environmental tests, with nodeterioration of the recording layer due to oxidation and no change ofthe mechanical properties of the recording layer.

Furthermore, the above embodiments, have been explained by way ofexamples of a magneto-optical disk wherein the recording layer has athree-layer FAD structure. However, identifying information just aseasily can be recorded on a RAD type, a CAD type, or a double mask typemagneto-optical disk that can be reproduced with magnetically inducedsuper resolution, with a recording method of the above embodiments, sothat the copying of contents can be prevented, while maintainingexcellent detection signal properties.

Industrial Applicability

In accordance with the present invention identifying information(write-once information) easily can be recorded onto or reproduced fromoptical disks, the copying of contents can be prevented, which is usefulfor an apparatus for recording and reproducing optical disks with anaccent on copyright protection.

What is claimed is:
 1. A method for reproducing write-once informationfrom an optical disk (a) comprising a disk substrate, and a recordinglayer on the disk substrate, the recording layer including a magneticfilm with a magnetic anisotropy in a direction perpendicular to asurface of the magnetic film; and (b) storing write-once informationformed by first recording areas and second recording areas in apre-determined portion of said recording layer, the first and secondrecording areas having different magnetic anisotropies in a directionperpendicular to a surface of the magnetic film; the method comprising:irradiating linearly polarized laser light onto said pre-determinedportion; and detecting a rotational change in a polarization orientationof light reflected from the optical disk or light transmitted throughthe optical disk, the rotational change being caused depending on whichof the first recording area and the second recording area is irradiatedwith the linearly polarized laser light, the rotational change occurringbetween +θk and approximately
 0. 2. The reproducing method according toclaim 1, wherein the linearly polarized laser light is irradiated ontosaid pre-determined portion after magnetizing the recording layer ofsaid pre-determined portion in one step by applying a magnetic fieldthat is larger than a coercive force of the recording layer in saidpre-determined portion.
 3. The reproducing method according to claim 1,wherein the linearly polarized laser light is irradiated onto saidpre-determined portion after aligning a magnetization of said recordinglayer of said pre-determined portion by applying a unidirectionalmagnetic field to said pre-determined portion while increasing thetemperature of said recording layer in said pre-determined portion abovethe Curie temperature by irradiating laser light of constant luminousenergy.
 4. A method for reproducing write-once information from anoptical disk (a) comprising a disk substrate, and a recording layer onthe disk substrate, the recording layer including a magnetic film with amagnetic anisotropy in a direction perpendicular to a surface of themagnetic film; and (b) capable of storing write-once information formedby first recording areas and second recording areas in a pre-determinedportion of said recording layer, the first and second recording areashaving different magnetic anisotropies in a direction perpendicular to asurface of the magnetic film; the method comprising: irradiatinglinearly polarized laser light onto said pre-determined portion; anddetecting a rotational change in a polarization orientation of lightreflected from the optical disk or light transmitted through the opticaldisk, the rotational change being caused depending on which of the firstrecording area and the second recording area is irradiated with thelinearly polarized laser light, the rotational change occurring between+θk and approximately
 0. 5. The reproducing method according to claim 4,wherein the linearly polarized laser light is irradiated onto saidpre-determined portion after magnetizing the recoding layer of saidpre-determined portion in one step by applying a magnetic field that islarger than a coercive force of the recording layer in saidpre-determined portion.
 6. The reproducing method according to claim 4,wherein the linearly polarized laser light is irradiated onto saidpre-determined portion after aligning a magnetization of said recordinglayer of said pre-determined portion by applying a unidirectionalmagnetic field to said pre-determined portion while increasing atemperature of said recording layer in said pre-determined portion abovea Curie temperature by irradiating laser light of constant luminousenergy.